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 $146.72   10.846%   $162.6333   $162.63   $162.65   $162.60  
  Purchase #2 $151.94   13.803%   $172.9123   $172.91   $172.90   $172.90  
  Purchase #3 $110.69   8.323%   $119.9027   $119.90   $119.90   $119.90  
  Purchase #4 $91.68   4.464%   $95.7726   $95.77   $95.75   $95.80  
  Purchase #5 $86.93   9.468%   $95.1605   $95.16   $95.15   $95.20  
  Purchase #6 $85.25   8.194%   $92.2354   $92.24   $92.25   $92.20  
  Purchase #7 $53.49   4.861%   $56.0901   $56.09   $56.10   $56.10  
  7 purchase totals = $726.70       $794.7069   $794.70   $794.70   $794.70