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 $88.80   4.559%   $92.8484   $92.85   $92.85   $92.80  
  Purchase #2 $72.90   4.453%   $76.1462   $76.15   $76.15   $76.10  
  Purchase #3 $221.71   12.379%   $249.1555   $249.16   $249.15   $249.20  
  Purchase #4 $248.33   6.289%   $263.9475   $263.95   $263.95   $263.90  
  Purchase #5 $44.98   8.519%   $48.8118   $48.81   $48.80   $48.80  
  Purchase #6 $51.68   6.670%   $55.1271   $55.13   $55.15   $55.10  
  Purchase #7 $217.50   13.450%   $246.7538   $246.75   $246.75   $246.80  
  7 purchase totals = $945.90       $1,032.7903   $1,032.80   $1,032.80   $1,032.70