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 $159.69   4.699%   $167.1938   $167.19   $167.20   $167.20  
  Purchase #2 $26.87   12.163%   $30.1382   $30.14   $30.15   $30.10  
  Purchase #3 $225.76   13.733%   $256.7636   $256.76   $256.75   $256.80  
  Purchase #4 $94.60   7.575%   $101.766   $101.77   $101.75   $101.80  
  Purchase #5 $30.69   5.412%   $32.3509   $32.35   $32.35   $32.40  
  Purchase #6 $95.82   11.245%   $106.595   $106.60   $106.60   $106.60  
  Purchase #7 $155.91   7.499%   $167.6017   $167.60   $167.60   $167.60  
  7 purchase totals = $789.34       $862.4092   $862.41   $862.40   $862.50