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 $180.68   12.361%   $203.0139   $203.01   $203.00   $203.00  
  Purchase #2 $140.96   8.119%   $152.4045   $152.40   $152.40   $152.40  
  Purchase #3 $245.90   7.345%   $263.9614   $263.96   $263.95   $264.00  
  Purchase #4 $227.47   3.818%   $236.1548   $236.15   $236.15   $236.20  
  Purchase #5 $223.42   9.492%   $244.627   $244.63   $244.65   $244.60  
  Purchase #6 $213.89   4.701%   $223.945   $223.95   $223.95   $223.90  
  Purchase #7 $235.71   5.428%   $248.5043   $248.50   $248.50   $248.50  
  7 purchase totals = $1,468.03       $1,572.6109   $1,572.60   $1,572.60   $1,572.60