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 $59.39   11.555%   $66.2525   $66.25   $66.25   $66.30  
  Purchase #2 $135.66   7.795%   $146.2347   $146.23   $146.25   $146.20  
  Purchase #3 $216.48   8.215%   $234.2638   $234.26   $234.25   $234.30  
  Purchase #4 $221.31   13.281%   $250.7022   $250.70   $250.70   $250.70  
  Purchase #5 $61.85   7.537%   $66.5116   $66.51   $66.50   $66.50  
  Purchase #6 $218.77   8.823%   $238.0721   $238.07   $238.05   $238.10  
  Purchase #7 $48.55   12.781%   $54.7552   $54.76   $54.75   $54.80  
  7 purchase totals = $962.01       $1,056.7921   $1,056.78   $1,056.75   $1,056.90