Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $236.65   7.538%   $254.4887   $254.49   $254.50   $254.50  
  Purchase #2 $53.82   12.625%   $60.6148   $60.61   $60.60   $60.60  
  Purchase #3 $199.82   8.484%   $216.7727   $216.77   $216.75   $216.80  
  Purchase #4 $207.48   9.759%   $227.728   $227.73   $227.75   $227.70  
  Purchase #5 $230.25   7.451%   $247.4059   $247.41   $247.40   $247.40  
  Purchase #6 $179.96   8.161%   $194.6465   $194.65   $194.65   $194.60  
  Purchase #7 $230.73   10.215%   $254.2991   $254.30   $254.30   $254.30  
  7 purchase totals = $1,338.71       $1,455.9557   $1,455.96   $1,455.95   $1,455.90