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 $48.95   5.377%   $51.582   $51.58   $51.60   $51.60  
  Purchase #2 $20.84   13.156%   $23.5817   $23.58   $23.60   $23.60  
  Purchase #3 $123.25   3.634%   $127.7289   $127.73   $127.75   $127.70  
  Purchase #4 $92.35   12.806%   $104.1763   $104.18   $104.20   $104.20  
  Purchase #5 $73.35   12.576%   $82.5745   $82.57   $82.55   $82.60  
  Purchase #6 $71.41   13.620%   $81.136   $81.14   $81.15   $81.10  
  Purchase #7 $227.38   7.332%   $244.0515   $244.05   $244.05   $244.10  
  7 purchase totals = $657.53       $714.8309   $714.83   $714.90   $714.90