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 $59.67   6.798%   $63.7264   $63.73   $63.75   $63.70  
  Purchase #2 $42.85   9.375%   $46.8672   $46.87   $46.85   $46.90  
  Purchase #3 $248.77   13.478%   $282.2992   $282.30   $282.30   $282.30  
  Purchase #4 $66.84   4.541%   $69.8752   $69.88   $69.90   $69.90  
  Purchase #5 $140.95   13.448%   $159.905   $159.91   $159.90   $159.90  
  Purchase #6 $106.91   13.695%   $121.5513   $121.55   $121.55   $121.60  
  Purchase #7 $66.25   11.865%   $74.1106   $74.11   $74.10   $74.10  
  7 purchase totals = $732.24       $818.3349   $818.35   $818.35   $818.40