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 $36.64   13.533%   $41.5985   $41.60   $41.60   $41.60  
  Purchase #2 $106.85   11.531%   $119.1709   $119.17   $119.15   $119.20  
  Purchase #3 $123.35   10.106%   $135.8158   $135.82   $135.80   $135.80  
  Purchase #4 $53.33   3.828%   $55.3715   $55.37   $55.35   $55.40  
  Purchase #5 $55.93   9.109%   $61.0247   $61.02   $61.00   $61.00  
  Purchase #6 $188.74   8.461%   $204.7093   $204.71   $204.70   $204.70  
  Purchase #7 $224.99   9.628%   $246.652   $246.65   $246.65   $246.70  
  7 purchase totals = $789.83       $864.3427   $864.34   $864.25   $864.40