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 $95.37   8.276%   $103.2628   $103.26   $103.25   $103.30  
  Purchase #2 $58.97   13.141%   $66.7192   $66.72   $66.70   $66.70  
  Purchase #3 $82.80   9.581%   $90.7331   $90.73   $90.75   $90.70  
  Purchase #4 $184.26   11.346%   $205.1661   $205.17   $205.15   $205.20  
  Purchase #5 $111.77   13.491%   $126.8489   $126.85   $126.85   $126.80  
  Purchase #6 $157.69   9.257%   $172.2874   $172.29   $172.30   $172.30  
  Purchase #7 $64.37   13.536%   $73.0831   $73.08   $73.10   $73.10  
  7 purchase totals = $755.23       $838.1006   $838.10   $838.10   $838.10