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 $67.94   11.838%   $75.9827   $75.98   $76.00   $76.00  
  Purchase #2 $57.81   11.453%   $64.431   $64.43   $64.45   $64.40  
  Purchase #3 $243.90   8.427%   $264.4535   $264.45   $264.45   $264.50  
  Purchase #4 $181.59   6.686%   $193.7311   $193.73   $193.75   $193.70  
  Purchase #5 $25.76   9.823%   $28.2904   $28.29   $28.30   $28.30  
  Purchase #6 $69.28   5.251%   $72.9179   $72.92   $72.90   $72.90  
  Purchase #7 $76.73   3.109%   $79.1155   $79.12   $79.10   $79.10  
  7 purchase totals = $723.01       $778.9221   $778.92   $778.95   $778.90