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 $56.67   5.140%   $59.5828   $59.58   $59.60   $59.60  
  Purchase #2 $44.87   11.653%   $50.0987   $50.10   $50.10   $50.10  
  Purchase #3 $110.63   6.838%   $118.1949   $118.19   $118.20   $118.20  
  Purchase #4 $163.59   8.734%   $177.878   $177.88   $177.90   $177.90  
  Purchase #5 $143.97   12.491%   $161.9533   $161.95   $161.95   $162.00  
  Purchase #6 $104.75   5.788%   $110.8129   $110.81   $110.80   $110.80  
  Purchase #7 $196.33   10.138%   $216.2339   $216.23   $216.25   $216.20  
  7 purchase totals = $820.81       $894.7545   $894.74   $894.80   $894.80