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 $250.39   4.347%   $261.2745   $261.27   $261.25   $261.30  
  Purchase #2 $56.96   13.187%   $64.4713   $64.47   $64.45   $64.50  
  Purchase #3 $27.60   9.847%   $30.3178   $30.32   $30.30   $30.30  
  Purchase #4 $243.47   6.519%   $259.3418   $259.34   $259.35   $259.30  
  Purchase #5 $62.91   5.485%   $66.3606   $66.36   $66.35   $66.40  
  Purchase #6 $97.46   11.339%   $108.511   $108.51   $108.50   $108.50  
  Purchase #7 $113.81   11.569%   $126.9767   $126.98   $127.00   $127.00  
  7 purchase totals = $852.60       $917.2537   $917.25   $917.20   $917.30