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 $73.94   13.286%   $83.7637   $83.76   $83.75   $83.80  
  Purchase #2 $24.49   11.217%   $27.237   $27.24   $27.25   $27.20  
  Purchase #3 $75.39   12.307%   $84.6682   $84.67   $84.65   $84.70  
  Purchase #4 $42.75   11.682%   $47.7441   $47.74   $47.75   $47.70  
  Purchase #5 $250.47   6.547%   $266.8683   $266.87   $266.85   $266.90  
  Purchase #6 $138.47   9.533%   $151.6703   $151.67   $151.65   $151.70  
  Purchase #7 $56.72   13.309%   $64.2689   $64.27   $64.25   $64.30  
  7 purchase totals = $662.23       $726.2205   $726.22   $726.15   $726.30