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 $61.38   8.143%   $66.3782   $66.38   $66.40   $66.40  
  Purchase #2 $40.85   12.706%   $46.0404   $46.04   $46.05   $46.00  
  Purchase #3 $70.50   4.545%   $73.7042   $73.70   $73.70   $73.70  
  Purchase #4 $87.42   6.728%   $93.3016   $93.30   $93.30   $93.30  
  Purchase #5 $58.45   4.463%   $61.0586   $61.06   $61.05   $61.10  
  Purchase #6 $210.38   8.186%   $227.6017   $227.60   $227.60   $227.60  
  Purchase #7 $149.51   7.436%   $160.6276   $160.63   $160.65   $160.60  
  7 purchase totals = $678.49       $728.7123   $728.71   $728.75   $728.70