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 $59.60   3.692%   $61.8004   $61.80   $61.80   $61.80  
  Purchase #2 $215.78   9.347%   $235.949   $235.95   $235.95   $235.90  
  Purchase #3 $223.34   9.645%   $244.8811   $244.88   $244.90   $244.90  
  Purchase #4 $119.25   12.105%   $133.6852   $133.69   $133.70   $133.70  
  Purchase #5 $230.35   5.520%   $243.0653   $243.07   $243.05   $243.10  
  Purchase #6 $218.81   12.153%   $245.402   $245.40   $245.40   $245.40  
  Purchase #7 $94.50   11.650%   $105.5093   $105.51   $105.50   $105.50  
  7 purchase totals = $1,161.63       $1,270.2923   $1,270.30   $1,270.30   $1,270.30