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 $240.58   11.194%   $267.5105   $267.51   $267.50   $267.50  
  Purchase #2 $91.76   11.788%   $102.5767   $102.58   $102.60   $102.60  
  Purchase #3 $229.90   9.459%   $251.6462   $251.65   $251.65   $251.60  
  Purchase #4 $14.42   6.138%   $15.3051   $15.31   $15.30   $15.30  
  Purchase #5 $123.93   5.562%   $130.823   $130.82   $130.80   $130.80  
  Purchase #6 $153.82   6.275%   $163.4722   $163.47   $163.45   $163.50  
  Purchase #7 $89.65   10.428%   $98.9987   $99.00   $99.00   $99.00  
  7 purchase totals = $944.06       $1,030.3324   $1,030.34   $1,030.30   $1,030.30