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 $214.67   11.706%   $239.7993   $239.80   $239.80   $239.80  
  Purchase #2 $86.94   7.472%   $93.4362   $93.44   $93.45   $93.40  
  Purchase #3 $175.38   11.524%   $195.5908   $195.59   $195.60   $195.60  
  Purchase #4 $47.35   4.280%   $49.3766   $49.38   $49.40   $49.40  
  Purchase #5 $5.96   13.583%   $6.7695   $6.77   $6.75   $6.80  
  Purchase #6 $91.72   6.223%   $97.4277   $97.43   $97.45   $97.40  
  Purchase #7 $237.49   9.361%   $259.7214   $259.72   $259.70   $259.70  
  7 purchase totals = $859.51       $942.1215   $942.13   $942.15   $942.10