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 $67.62   5.693%   $71.4696   $71.47   $71.45   $71.50  
  Purchase #2 $229.35   7.359%   $246.2279   $246.23   $246.25   $246.20  
  Purchase #3 $221.95   9.298%   $242.5869   $242.59   $242.60   $242.60  
  Purchase #4 $110.71   13.549%   $125.7101   $125.71   $125.70   $125.70  
  Purchase #5 $151.66   4.208%   $158.0419   $158.04   $158.05   $158.00  
  Purchase #6 $207.50   5.785%   $219.5039   $219.50   $219.50   $219.50  
  Purchase #7 $224.62   11.200%   $249.7774   $249.78   $249.80   $249.80  
  7 purchase totals = $1,213.41       $1,313.3177   $1,313.32   $1,313.35   $1,313.30