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 $189.68   8.618%   $206.0266   $206.03   $206.05   $206.00  
  Purchase #2 $90.83   7.228%   $97.3952   $97.40   $97.40   $97.40  
  Purchase #3 $86.31   3.626%   $89.4396   $89.44   $89.45   $89.40  
  Purchase #4 $155.29   9.176%   $169.5394   $169.54   $169.55   $169.50  
  Purchase #5 $129.51   9.651%   $142.009   $142.01   $142.00   $142.00  
  Purchase #6 $167.87   8.757%   $182.5704   $182.57   $182.55   $182.60  
  Purchase #7 $65.76   5.616%   $69.4531   $69.45   $69.45   $69.50  
  7 purchase totals = $885.25       $956.4333   $956.44   $956.45   $956.40