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 $41.75   12.119%   $46.8097   $46.81   $46.80   $46.80  
  Purchase #2 $231.61   9.590%   $253.8214   $253.82   $253.80   $253.80  
  Purchase #3 $117.25   13.439%   $133.0072   $133.01   $133.00   $133.00  
  Purchase #4 $46.43   3.868%   $48.2259   $48.23   $48.25   $48.20  
  Purchase #5 $213.47   11.245%   $237.4747   $237.47   $237.45   $237.50  
  Purchase #6 $187.86   8.563%   $203.9465   $203.95   $203.95   $203.90  
  Purchase #7 $21.37   10.761%   $23.6696   $23.67   $23.65   $23.70  
  7 purchase totals = $859.74       $946.9550   $946.96   $946.90   $946.90