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 $182.43   11.720%   $203.8108   $203.81   $203.80   $203.80  
  Purchase #2 $88.53   4.773%   $92.7555   $92.76   $92.75   $92.80  
  Purchase #3 $119.78   10.614%   $132.4934   $132.49   $132.50   $132.50  
  Purchase #4 $48.61   11.442%   $54.172   $54.17   $54.15   $54.20  
  Purchase #5 $27.73   6.851%   $29.6298   $29.63   $29.65   $29.60  
  Purchase #6 $53.74   13.189%   $60.8278   $60.83   $60.85   $60.80  
  Purchase #7 $248.86   9.648%   $272.87   $272.87   $272.85   $272.90  
  7 purchase totals = $769.68       $846.5593   $846.56   $846.55   $846.60