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 $232.34   5.782%   $245.7739   $245.77   $245.75   $245.80  
  Purchase #2 $101.90   13.276%   $115.4282   $115.43   $115.45   $115.40  
  Purchase #3 $32.79   5.102%   $34.4629   $34.46   $34.45   $34.50  
  Purchase #4 $88.99   8.300%   $96.3762   $96.38   $96.40   $96.40  
  Purchase #5 $104.58   12.872%   $118.0415   $118.04   $118.05   $118.00  
  Purchase #6 $167.27   9.184%   $182.6321   $182.63   $182.65   $182.60  
  Purchase #7 $236.85   13.321%   $268.4008   $268.40   $268.40   $268.40  
  7 purchase totals = $964.72       $1,061.1156   $1,061.11   $1,061.15   $1,061.10