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 $205.69   9.271%   $224.7595   $224.76   $224.75   $224.80  
  Purchase #2 $181.70   8.505%   $197.1536   $197.15   $197.15   $197.20  
  Purchase #3 $190.84   11.762%   $213.2866   $213.29   $213.30   $213.30  
  Purchase #4 $242.55   4.549%   $253.5836   $253.58   $253.60   $253.60  
  Purchase #5 $154.35   3.581%   $159.8773   $159.88   $159.90   $159.90  
  Purchase #6 $249.74   5.339%   $263.0736   $263.07   $263.05   $263.10  
  Purchase #7 $101.53   3.202%   $104.781   $104.78   $104.80   $104.80  
  7 purchase totals = $1,326.40       $1,416.5152   $1,416.51   $1,416.55   $1,416.70