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 $34.54   8.353%   $37.4251   $37.43   $37.45   $37.40  
  Purchase #2 $5.47   10.375%   $6.0375   $6.04   $6.05   $6.00  
  Purchase #3 $76.73   9.439%   $83.9725   $83.97   $83.95   $84.00  
  Purchase #4 $179.70   6.157%   $190.7641   $190.76   $190.75   $190.80  
  Purchase #5 $68.76   10.176%   $75.757   $75.76   $75.75   $75.80  
  Purchase #6 $155.82   12.783%   $175.7385   $175.74   $175.75   $175.70  
  Purchase #7 $178.98   8.468%   $194.136   $194.14   $194.15   $194.10  
  7 purchase totals = $700.00       $763.8307   $763.84   $763.85   $763.80