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 $64.92   12.706%   $73.1687   $73.17   $73.15   $73.20  
  Purchase #2 $182.30   5.564%   $192.4432   $192.44   $192.45   $192.40  
  Purchase #3 $132.33   5.872%   $140.1004   $140.10   $140.10   $140.10  
  Purchase #4 $245.63   13.668%   $279.2027   $279.20   $279.20   $279.20  
  Purchase #5 $52.90   13.471%   $60.0262   $60.03   $60.05   $60.00  
  Purchase #6 $133.56   13.335%   $151.3702   $151.37   $151.35   $151.40  
  Purchase #7 $152.52   3.135%   $157.3015   $157.30   $157.30   $157.30  
  7 purchase totals = $964.16       $1,053.6129   $1,053.61   $1,053.60   $1,053.60