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 $217.95   13.312%   $246.9635   $246.96   $246.95   $247.00  
  Purchase #2 $233.57   5.413%   $246.2131   $246.21   $246.20   $246.20  
  Purchase #3 $250.84   11.692%   $280.1682   $280.17   $280.15   $280.20  
  Purchase #4 $219.75   8.224%   $237.8222   $237.82   $237.80   $237.80  
  Purchase #5 $69.33   9.829%   $76.1444   $76.14   $76.15   $76.10  
  Purchase #6 $243.92   3.761%   $253.0938   $253.09   $253.10   $253.10  
  Purchase #7 $108.81   3.853%   $113.0024   $113.00   $113.00   $113.00  
  7 purchase totals = $1,344.17       $1,453.4076   $1,453.39   $1,453.35   $1,453.40