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 $63.77   11.614%   $71.1762   $71.18   $71.20   $71.20  
  Purchase #2 $91.80   10.389%   $101.3371   $101.34   $101.35   $101.30  
  Purchase #3 $186.25   4.720%   $195.041   $195.04   $195.05   $195.00  
  Purchase #4 $38.62   5.213%   $40.6333   $40.63   $40.65   $40.60  
  Purchase #5 $161.80   5.313%   $170.3964   $170.40   $170.40   $170.40  
  Purchase #6 $231.67   12.551%   $260.7469   $260.75   $260.75   $260.70  
  Purchase #7 $82.37   10.717%   $91.1976   $91.20   $91.20   $91.20  
  7 purchase totals = $856.28       $930.5285   $930.54   $930.60   $930.40