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 $61.66   11.114%   $68.5129   $68.51   $68.50   $68.50  
  Purchase #2 $117.87   8.652%   $128.0681   $128.07   $128.05   $128.10  
  Purchase #3 $137.34   10.137%   $151.2622   $151.26   $151.25   $151.30  
  Purchase #4 $99.40   13.467%   $112.7862   $112.79   $112.80   $112.80  
  Purchase #5 $107.86   5.624%   $113.926   $113.93   $113.95   $113.90  
  Purchase #6 $87.89   9.350%   $96.1077   $96.11   $96.10   $96.10  
  Purchase #7 $92.55   3.545%   $95.8309   $95.83   $95.85   $95.80  
  7 purchase totals = $704.57       $766.4940   $766.50   $766.50   $766.50