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 $206.69   3.758%   $214.4574   $214.46   $214.45   $214.50  
  Purchase #2 $88.60   4.211%   $92.3309   $92.33   $92.35   $92.30  
  Purchase #3 $46.90   5.645%   $49.5475   $49.55   $49.55   $49.50  
  Purchase #4 $92.92   13.384%   $105.3564   $105.36   $105.35   $105.40  
  Purchase #5 $45.60   4.446%   $47.6274   $47.63   $47.65   $47.60  
  Purchase #6 $154.70   13.131%   $175.0137   $175.01   $175.00   $175.00  
  Purchase #7 $166.98   9.848%   $183.4242   $183.42   $183.40   $183.40  
  7 purchase totals = $802.39       $867.7575   $867.76   $867.75   $867.70