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 $24.50   7.755%   $26.4   $26.40   $26.40   $26.40  
  Purchase #2 $55.34   9.640%   $60.6748   $60.67   $60.65   $60.70  
  Purchase #3 $75.94   9.734%   $83.332   $83.33   $83.35   $83.30  
  Purchase #4 $185.78   5.204%   $195.448   $195.45   $195.45   $195.40  
  Purchase #5 $138.67   9.317%   $151.5899   $151.59   $151.60   $151.60  
  Purchase #6 $119.28   11.267%   $132.7193   $132.72   $132.70   $132.70  
  Purchase #7 $83.61   8.477%   $90.6976   $90.70   $90.70   $90.70  
  7 purchase totals = $683.12       $740.8616   $740.86   $740.85   $740.80