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 $48.72   12.617%   $54.867   $54.87   $54.85   $54.90  
  Purchase #2 $217.44   12.165%   $243.8916   $243.89   $243.90   $243.90  
  Purchase #3 $123.54   4.671%   $129.3106   $129.31   $129.30   $129.30  
  Purchase #4 $229.78   6.397%   $244.479   $244.48   $244.50   $244.50  
  Purchase #5 $78.74   10.182%   $86.7573   $86.76   $86.75   $86.80  
  Purchase #6 $22.30   3.300%   $23.0359   $23.04   $23.05   $23.00  
  Purchase #7 $162.94   6.366%   $173.3128   $173.31   $173.30   $173.30  
  7 purchase totals = $883.46       $955.6542   $955.66   $955.65   $955.70