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 $136.98   6.709%   $146.17   $146.17   $146.15   $146.20  
  Purchase #2 $213.58   9.521%   $233.915   $233.92   $233.90   $233.90  
  Purchase #3 $195.68   4.436%   $204.3604   $204.36   $204.35   $204.40  
  Purchase #4 $11.66   10.762%   $12.9148   $12.91   $12.90   $12.90  
  Purchase #5 $32.47   11.354%   $36.1566   $36.16   $36.15   $36.20  
  Purchase #6 $197.78   9.406%   $216.3832   $216.38   $216.40   $216.40  
  Purchase #7 $60.87   6.737%   $64.9708   $64.97   $64.95   $65.00  
  7 purchase totals = $849.02       $914.8708   $914.87   $914.80   $915.00