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 $82.86   11.536%   $92.4187   $92.42   $92.40   $92.40  
  Purchase #2 $173.87   5.120%   $182.7721   $182.77   $182.75   $182.80  
  Purchase #3 $178.97   7.624%   $192.6147   $192.61   $192.60   $192.60  
  Purchase #4 $76.40   3.761%   $79.2734   $79.27   $79.25   $79.30  
  Purchase #5 $57.67   5.479%   $60.8297   $60.83   $60.85   $60.80  
  Purchase #6 $216.88   9.653%   $237.8154   $237.82   $237.80   $237.80  
  Purchase #7 $199.38   5.259%   $209.8654   $209.87   $209.85   $209.90  
  7 purchase totals = $986.03       $1,055.5894   $1,055.59   $1,055.50   $1,055.60