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 $75.90   8.532%   $82.3758   $82.38   $82.40   $82.40  
  Purchase #2 $149.46   12.163%   $167.6388   $167.64   $167.65   $167.60  
  Purchase #3 $103.92   8.123%   $112.3614   $112.36   $112.35   $112.40  
  Purchase #4 $182.31   6.339%   $193.8666   $193.87   $193.85   $193.90  
  Purchase #5 $113.58   3.652%   $117.7279   $117.73   $117.75   $117.70  
  Purchase #6 $93.50   4.172%   $97.4008   $97.40   $97.40   $97.40  
  Purchase #7 $12.75   10.632%   $14.1056   $14.11   $14.10   $14.10  
  7 purchase totals = $731.42       $785.4769   $785.49   $785.50   $785.50