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 $215.82   11.561%   $240.771   $240.77   $240.75   $240.80  
  Purchase #2 $35.71   4.331%   $37.2566   $37.26   $37.25   $37.30  
  Purchase #3 $191.73   11.787%   $214.3292   $214.33   $214.35   $214.30  
  Purchase #4 $159.40   12.181%   $178.8165   $178.82   $178.80   $178.80  
  Purchase #5 $87.60   11.799%   $97.9359   $97.94   $97.95   $97.90  
  Purchase #6 $118.92   11.324%   $132.3865   $132.39   $132.40   $132.40  
  Purchase #7 $155.84   13.731%   $177.2384   $177.24   $177.25   $177.20  
  7 purchase totals = $965.02       $1,078.7341   $1,078.75   $1,078.75   $1,078.70