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 $180.38   3.680%   $187.018   $187.02   $187.00   $187.00  
  Purchase #2 $201.51   12.623%   $226.9466   $226.95   $226.95   $226.90  
  Purchase #3 $250.82   6.443%   $266.9803   $266.98   $267.00   $267.00  
  Purchase #4 $45.90   6.172%   $48.7329   $48.73   $48.75   $48.70  
  Purchase #5 $163.32   11.533%   $182.1557   $182.16   $182.15   $182.20  
  Purchase #6 $30.49   12.530%   $34.3104   $34.31   $34.30   $34.30  
  Purchase #7 $86.42   11.317%   $96.2002   $96.20   $96.20   $96.20  
  7 purchase totals = $958.84       $1,042.3441   $1,042.35   $1,042.35   $1,042.30