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 $129.66   10.516%   $143.295   $143.30   $143.30   $143.30  
  Purchase #2 $60.68   10.187%   $66.8615   $66.86   $66.85   $66.90  
  Purchase #3 $245.49   3.256%   $253.4832   $253.48   $253.50   $253.50  
  Purchase #4 $161.84   13.145%   $183.1139   $183.11   $183.10   $183.10  
  Purchase #5 $13.45   11.249%   $14.963   $14.96   $14.95   $15.00  
  Purchase #6 $247.26   5.466%   $260.7752   $260.78   $260.80   $260.80  
  Purchase #7 $229.41   7.137%   $245.783   $245.78   $245.80   $245.80  
  7 purchase totals = $1,087.79       $1,168.2748   $1,168.27   $1,168.30   $1,168.40