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 $54.78   7.221%   $58.7357   $58.74   $58.75   $58.70  
  Purchase #2 $110.50   5.867%   $116.983   $116.98   $117.00   $117.00  
  Purchase #3 $149.98   9.790%   $164.663   $164.66   $164.65   $164.70  
  Purchase #4 $187.44   13.547%   $212.8325   $212.83   $212.85   $212.80  
  Purchase #5 $62.25   11.457%   $69.382   $69.38   $69.40   $69.40  
  Purchase #6 $224.73   13.857%   $255.8708   $255.87   $255.85   $255.90  
  Purchase #7 $67.66   11.599%   $75.5079   $75.51   $75.50   $75.50  
  7 purchase totals = $857.34       $953.9749   $953.97   $954.00   $954.00