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 $216.43   12.835%   $244.2088   $244.21   $244.20   $244.20  
  Purchase #2 $144.54   10.530%   $159.7601   $159.76   $159.75   $159.80  
  Purchase #3 $243.56   12.819%   $274.782   $274.78   $274.80   $274.80  
  Purchase #4 $171.99   13.458%   $195.1364   $195.14   $195.15   $195.10  
  Purchase #5 $58.98   13.517%   $66.9523   $66.95   $66.95   $67.00  
  Purchase #6 $204.44   5.131%   $214.9298   $214.93   $214.95   $214.90  
  Purchase #7 $43.43   7.302%   $46.6013   $46.60   $46.60   $46.60  
  7 purchase totals = $1,083.37       $1,202.3707   $1,202.37   $1,202.40   $1,202.40