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 $112.70   3.153%   $116.2534   $116.25   $116.25   $116.30  
  Purchase #2 $106.57   8.791%   $115.9386   $115.94   $115.95   $115.90  
  Purchase #3 $52.40   4.380%   $54.6951   $54.70   $54.70   $54.70  
  Purchase #4 $93.57   12.739%   $105.4899   $105.49   $105.50   $105.50  
  Purchase #5 $162.38   8.412%   $176.0394   $176.04   $176.05   $176.00  
  Purchase #6 $214.34   8.237%   $231.9952   $232.00   $232.00   $232.00  
  Purchase #7 $153.53   12.509%   $172.7351   $172.74   $172.75   $172.70  
  7 purchase totals = $895.49       $973.1467   $973.16   $973.20   $973.10