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 $88.50   10.160%   $97.4916   $97.49   $97.50   $97.50  
  Purchase #2 $61.63   8.140%   $66.6467   $66.65   $66.65   $66.60  
  Purchase #3 $194.28   4.339%   $202.7098   $202.71   $202.70   $202.70  
  Purchase #4 $6.56   5.305%   $6.908   $6.91   $6.90   $6.90  
  Purchase #5 $133.66   9.706%   $146.633   $146.63   $146.65   $146.60  
  Purchase #6 $93.39   3.383%   $96.5494   $96.55   $96.55   $96.50  
  Purchase #7 $6.26   8.808%   $6.8114   $6.81   $6.80   $6.80  
  7 purchase totals = $584.28       $623.7499   $623.75   $623.75   $623.60