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 $204.54   4.504%   $213.7525   $213.75   $213.75   $213.80  
  Purchase #2 $64.71   3.532%   $66.9956   $67.00   $67.00   $67.00  
  Purchase #3 $111.67   13.549%   $126.8002   $126.80   $126.80   $126.80  
  Purchase #4 $64.47   3.838%   $66.9444   $66.94   $66.95   $66.90  
  Purchase #5 $167.60   12.114%   $187.9031   $187.90   $187.90   $187.90  
  Purchase #6 $18.72   9.118%   $20.4269   $20.43   $20.45   $20.40  
  Purchase #7 $176.94   10.296%   $195.1577   $195.16   $195.15   $195.20  
  7 purchase totals = $808.65       $877.9804   $877.98   $878.00   $878.00