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 $68.45   7.178%   $73.3633   $73.36   $73.35   $73.40  
  Purchase #2 $213.76   10.113%   $235.3775   $235.38   $235.40   $235.40  
  Purchase #3 $103.70   3.108%   $106.923   $106.92   $106.90   $106.90  
  Purchase #4 $19.71   5.678%   $20.8291   $20.83   $20.85   $20.80  
  Purchase #5 $70.44   11.151%   $78.2948   $78.29   $78.30   $78.30  
  Purchase #6 $154.26   8.240%   $166.971   $166.97   $166.95   $167.00  
  Purchase #7 $57.57   7.153%   $61.688   $61.69   $61.70   $61.70  
  7 purchase totals = $687.89       $743.4467   $743.44   $743.45   $743.50