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 $209.51   8.128%   $226.539   $226.54   $226.55   $226.50  
  Purchase #2 $151.53   3.256%   $156.4638   $156.46   $156.45   $156.50  
  Purchase #3 $67.54   3.185%   $69.6911   $69.69   $69.70   $69.70  
  Purchase #4 $190.45   8.177%   $206.0231   $206.02   $206.00   $206.00  
  Purchase #5 $24.44   9.798%   $26.8346   $26.83   $26.85   $26.80  
  Purchase #6 $26.94   7.849%   $29.0545   $29.05   $29.05   $29.10  
  Purchase #7 $47.97   7.130%   $51.3903   $51.39   $51.40   $51.40  
  7 purchase totals = $718.38       $765.9964   $765.98   $766.00   $766.00