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 $57.48   11.698%   $64.204   $64.20   $64.20   $64.20  
  Purchase #2 $135.45   8.505%   $146.97   $146.97   $146.95   $147.00  
  Purchase #3 $139.95   12.852%   $157.9364   $157.94   $157.95   $157.90  
  Purchase #4 $126.92   12.481%   $142.7609   $142.76   $142.75   $142.80  
  Purchase #5 $32.37   12.269%   $36.3415   $36.34   $36.35   $36.30  
  Purchase #6 $167.37   9.135%   $182.6592   $182.66   $182.65   $182.70  
  Purchase #7 $158.51   10.340%   $174.8999   $174.90   $174.90   $174.90  
  7 purchase totals = $818.05       $905.7719   $905.77   $905.75   $905.80