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 $249.69   9.477%   $273.3531   $273.35   $273.35   $273.40  
  Purchase #2 $84.50   7.157%   $90.5477   $90.55   $90.55   $90.50  
  Purchase #3 $58.93   7.155%   $63.1464   $63.15   $63.15   $63.10  
  Purchase #4 $125.54   9.761%   $137.794   $137.79   $137.80   $137.80  
  Purchase #5 $133.44   8.282%   $144.4915   $144.49   $144.50   $144.50  
  Purchase #6 $111.79   12.299%   $125.5391   $125.54   $125.55   $125.50  
  Purchase #7 $201.32   9.782%   $221.0131   $221.01   $221.00   $221.00  
  7 purchase totals = $965.21       $1,055.8849   $1,055.88   $1,055.90   $1,055.80