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 $84.54   12.592%   $95.1853   $95.19   $95.20   $95.20  
  Purchase #2 $146.98   5.733%   $155.4064   $155.41   $155.40   $155.40  
  Purchase #3 $127.58   5.796%   $134.9745   $134.97   $134.95   $135.00  
  Purchase #4 $68.71   10.233%   $75.7411   $75.74   $75.75   $75.70  
  Purchase #5 $189.41   11.657%   $211.4895   $211.49   $211.50   $211.50  
  Purchase #6 $95.43   12.232%   $107.103   $107.10   $107.10   $107.10  
  Purchase #7 $197.97   6.104%   $210.0541   $210.05   $210.05   $210.10  
  7 purchase totals = $910.62       $989.9539   $989.95   $989.95   $990.00