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 $82.39   13.116%   $93.1963   $93.20   $93.20   $93.20  
  Purchase #2 $179.30   8.484%   $194.5118   $194.51   $194.50   $194.50  
  Purchase #3 $34.81   6.474%   $37.0636   $37.06   $37.05   $37.10  
  Purchase #4 $245.89   5.811%   $260.1787   $260.18   $260.20   $260.20  
  Purchase #5 $201.81   8.393%   $218.7479   $218.75   $218.75   $218.70  
  Purchase #6 $66.34   8.340%   $71.8728   $71.87   $71.85   $71.90  
  Purchase #7 $103.98   6.713%   $110.9602   $110.96   $110.95   $111.00  
  7 purchase totals = $914.52       $986.5313   $986.53   $986.50   $986.60