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 $88.43   8.131%   $95.6202   $95.62   $95.60   $95.60  
  Purchase #2 $245.69   12.699%   $276.8902   $276.89   $276.90   $276.90  
  Purchase #3 $170.63   7.370%   $183.2054   $183.21   $183.20   $183.20  
  Purchase #4 $126.30   10.687%   $139.7977   $139.80   $139.80   $139.80  
  Purchase #5 $126.71   3.485%   $131.1258   $131.13   $131.15   $131.10  
  Purchase #6 $19.47   11.135%   $21.638   $21.64   $21.65   $21.60  
  Purchase #7 $67.51   4.465%   $70.5243   $70.52   $70.50   $70.50  
  7 purchase totals = $844.74       $918.8016   $918.81   $918.80   $918.70