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 $57.86   11.626%   $64.5868   $64.59   $64.60   $64.60  
  Purchase #2 $111.59   5.449%   $117.6705   $117.67   $117.65   $117.70  
  Purchase #3 $237.28   4.404%   $247.7298   $247.73   $247.75   $247.70  
  Purchase #4 $177.63   7.680%   $191.272   $191.27   $191.25   $191.30  
  Purchase #5 $140.90   8.533%   $152.923   $152.92   $152.90   $152.90  
  Purchase #6 $9.36   10.403%   $10.3337   $10.33   $10.35   $10.30  
  Purchase #7 $193.71   8.503%   $210.1812   $210.18   $210.20   $210.20  
  7 purchase totals = $928.33       $994.6970   $994.69   $994.70   $994.70