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 $214.51   6.541%   $228.5411   $228.54   $228.55   $228.50  
  Purchase #2 $248.28   7.462%   $266.8067   $266.81   $266.80   $266.80  
  Purchase #3 $88.73   4.703%   $92.903   $92.90   $92.90   $92.90  
  Purchase #4 $44.83   12.409%   $50.393   $50.39   $50.40   $50.40  
  Purchase #5 $43.51   7.355%   $46.7102   $46.71   $46.70   $46.70  
  Purchase #6 $85.99   7.648%   $92.5665   $92.57   $92.55   $92.60  
  Purchase #7 $238.89   8.561%   $259.3414   $259.34   $259.35   $259.30  
  7 purchase totals = $964.74       $1,037.2619   $1,037.26   $1,037.25   $1,037.20