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 $15.63   6.706%   $16.6781   $16.68   $16.70   $16.70  
  Purchase #2 $45.69   4.177%   $47.5985   $47.60   $47.60   $47.60  
  Purchase #3 $187.39   7.677%   $201.7759   $201.78   $201.80   $201.80  
  Purchase #4 $53.88   10.423%   $59.4959   $59.50   $59.50   $59.50  
  Purchase #5 $242.39   11.245%   $269.6468   $269.65   $269.65   $269.60  
  Purchase #6 $171.85   6.549%   $183.1045   $183.10   $183.10   $183.10  
  Purchase #7 $116.75   6.569%   $124.4193   $124.42   $124.40   $124.40  
  7 purchase totals = $833.58       $902.7190   $902.73   $902.75   $902.70