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 $64.45   13.797%   $73.3422   $73.34   $73.35   $73.30  
  Purchase #2 $191.70   7.573%   $206.2174   $206.22   $206.20   $206.20  
  Purchase #3 $187.96   13.289%   $212.938   $212.94   $212.95   $212.90  
  Purchase #4 $22.32   8.489%   $24.2147   $24.21   $24.20   $24.20  
  Purchase #5 $188.89   3.561%   $195.6164   $195.62   $195.60   $195.60  
  Purchase #6 $157.66   4.470%   $164.7074   $164.71   $164.70   $164.70  
  Purchase #7 $46.73   3.183%   $48.2174   $48.22   $48.20   $48.20  
  7 purchase totals = $859.71       $925.2535   $925.26   $925.20   $925.10