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 $44.96   5.752%   $47.5461   $47.55   $47.55   $47.50  
  Purchase #2 $108.57   10.319%   $119.7733   $119.77   $119.75   $119.80  
  Purchase #3 $64.60   10.476%   $71.3675   $71.37   $71.35   $71.40  
  Purchase #4 $240.89   3.134%   $248.4395   $248.44   $248.45   $248.40  
  Purchase #5 $247.66   10.233%   $273.003   $273.00   $273.00   $273.00  
  Purchase #6 $79.63   4.158%   $82.941   $82.94   $82.95   $82.90  
  Purchase #7 $109.91   7.535%   $118.1917   $118.19   $118.20   $118.20  
  7 purchase totals = $896.22       $961.2621   $961.26   $961.25   $961.20