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 $64.68   5.864%   $68.4728   $68.47   $68.45   $68.50  
  Purchase #2 $161.26   13.577%   $183.1543   $183.15   $183.15   $183.20  
  Purchase #3 $244.89   6.298%   $260.3132   $260.31   $260.30   $260.30  
  Purchase #4 $159.41   3.399%   $164.8283   $164.83   $164.85   $164.80  
  Purchase #5 $246.43   13.262%   $279.1115   $279.11   $279.10   $279.10  
  Purchase #6 $202.43   11.362%   $225.4301   $225.43   $225.45   $225.40  
  Purchase #7 $224.29   11.309%   $249.655   $249.66   $249.65   $249.70  
  7 purchase totals = $1,303.39       $1,430.9652   $1,430.96   $1,430.95   $1,431.00