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 $66.62   4.142%   $69.3794   $69.38   $69.40   $69.40  
  Purchase #2 $111.92   10.808%   $124.0163   $124.02   $124.00   $124.00  
  Purchase #3 $62.36   12.439%   $70.117   $70.12   $70.10   $70.10  
  Purchase #4 $65.99   10.298%   $72.7857   $72.79   $72.80   $72.80  
  Purchase #5 $185.80   5.404%   $195.8406   $195.84   $195.85   $195.80  
  Purchase #6 $195.89   9.763%   $215.0147   $215.01   $215.00   $215.00  
  Purchase #7 $19.69   12.816%   $22.2135   $22.21   $22.20   $22.20  
  7 purchase totals = $708.27       $769.3672   $769.37   $769.35   $769.30