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 $163.32   13.136%   $184.7737   $184.77   $184.75   $184.80  
  Purchase #2 $57.99   13.707%   $65.9387   $65.94   $65.95   $65.90  
  Purchase #3 $92.48   10.551%   $102.2376   $102.24   $102.25   $102.20  
  Purchase #4 $241.60   10.156%   $266.1369   $266.14   $266.15   $266.10  
  Purchase #5 $195.98   4.534%   $204.8657   $204.87   $204.85   $204.90  
  Purchase #6 $155.74   13.229%   $176.3428   $176.34   $176.35   $176.30  
  Purchase #7 $210.71   10.761%   $233.3845   $233.38   $233.40   $233.40  
  7 purchase totals = $1,117.82       $1,233.6799   $1,233.68   $1,233.70   $1,233.60