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 $57.74   8.452%   $62.6202   $62.62   $62.60   $62.60  
  Purchase #2 $215.89   11.304%   $240.2942   $240.29   $240.30   $240.30  
  Purchase #3 $36.45   9.327%   $39.8497   $39.85   $39.85   $39.80  
  Purchase #4 $108.35   9.399%   $118.5338   $118.53   $118.55   $118.50  
  Purchase #5 $38.58   4.148%   $40.1803   $40.18   $40.20   $40.20  
  Purchase #6 $249.34   11.743%   $278.62   $278.62   $278.60   $278.60  
  Purchase #7 $236.33   3.379%   $244.3156   $244.32   $244.30   $244.30  
  7 purchase totals = $942.68       $1,024.4138   $1,024.41   $1,024.40   $1,024.30