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 $84.41   10.629%   $93.3819   $93.38   $93.40   $93.40  
  Purchase #2 $60.91   13.239%   $68.9739   $68.97   $68.95   $69.00  
  Purchase #3 $118.82   8.733%   $129.1966   $129.20   $129.20   $129.20  
  Purchase #4 $120.76   8.404%   $130.9087   $130.91   $130.90   $130.90  
  Purchase #5 $180.80   11.342%   $201.3063   $201.31   $201.30   $201.30  
  Purchase #6 $33.29   5.592%   $35.1516   $35.15   $35.15   $35.20  
  Purchase #7 $151.63   7.660%   $163.2449   $163.24   $163.25   $163.20  
  7 purchase totals = $750.62       $822.1639   $822.16   $822.15   $822.20