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 $83.73   12.271%   $94.0045   $94.00   $94.00   $94.00  
  Purchase #2 $106.46   3.803%   $110.5087   $110.51   $110.50   $110.50  
  Purchase #3 $244.78   8.130%   $264.6806   $264.68   $264.70   $264.70  
  Purchase #4 $58.57   9.749%   $64.28   $64.28   $64.30   $64.30  
  Purchase #5 $110.25   13.656%   $125.3057   $125.31   $125.30   $125.30  
  Purchase #6 $15.71   11.419%   $17.5039   $17.50   $17.50   $17.50  
  Purchase #7 $64.82   8.514%   $70.3388   $70.34   $70.35   $70.30  
  7 purchase totals = $684.32       $746.6222   $746.62   $746.65   $746.60