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 $73.59   3.281%   $76.0045   $76.00   $76.00   $76.00  
  Purchase #2 $72.42   5.316%   $76.2698   $76.27   $76.25   $76.30  
  Purchase #3 $89.59   4.488%   $93.6108   $93.61   $93.60   $93.60  
  Purchase #4 $35.93   9.555%   $39.3631   $39.36   $39.35   $39.40  
  Purchase #5 $97.68   11.274%   $108.6924   $108.69   $108.70   $108.70  
  Purchase #6 $101.56   10.173%   $111.8917   $111.89   $111.90   $111.90  
  Purchase #7 $121.65   3.113%   $125.437   $125.44   $125.45   $125.40  
  7 purchase totals = $592.42       $631.2693   $631.26   $631.25   $631.30