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 $248.65   11.224%   $276.5585   $276.56   $276.55   $276.60  
  Purchase #2 $130.60   11.224%   $145.2585   $145.26   $145.25   $145.30  
  Purchase #3 $19.88   8.639%   $21.5974   $21.60   $21.60   $21.60  
  Purchase #4 $44.63   13.184%   $50.514   $50.51   $50.50   $50.50  
  Purchase #5 $224.84   5.799%   $237.8785   $237.88   $237.90   $237.90  
  Purchase #6 $168.42   11.330%   $187.502   $187.50   $187.50   $187.50  
  Purchase #7 $110.34   4.773%   $115.6065   $115.61   $115.60   $115.60  
  7 purchase totals = $947.36       $1,034.9154   $1,034.92   $1,034.90   $1,035.00