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 $93.28   11.467%   $103.9764   $103.98   $104.00   $104.00  
  Purchase #2 $245.72   8.392%   $266.3408   $266.34   $266.35   $266.30  
  Purchase #3 $74.96   11.724%   $83.7483   $83.75   $83.75   $83.70  
  Purchase #4 $25.79   4.105%   $26.8487   $26.85   $26.85   $26.80  
  Purchase #5 $161.45   10.464%   $178.3441   $178.34   $178.35   $178.30  
  Purchase #6 $88.27   11.456%   $98.3822   $98.38   $98.40   $98.40  
  Purchase #7 $188.49   6.626%   $200.9793   $200.98   $201.00   $201.00  
  7 purchase totals = $877.96       $958.6198   $958.62   $958.70   $958.50