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 $250.49   5.234%   $263.6006   $263.60   $263.60   $263.60  
  Purchase #2 $146.32   4.761%   $153.2863   $153.29   $153.30   $153.30  
  Purchase #3 $161.68   3.583%   $167.473   $167.47   $167.45   $167.50  
  Purchase #4 $214.36   8.574%   $232.7392   $232.74   $232.75   $232.70  
  Purchase #5 $203.42   12.811%   $229.4801   $229.48   $229.50   $229.50  
  Purchase #6 $231.59   11.673%   $258.6235   $258.62   $258.60   $258.60  
  Purchase #7 $114.27   4.708%   $119.6498   $119.65   $119.65   $119.60  
  7 purchase totals = $1,322.13       $1,424.8525   $1,424.85   $1,424.85   $1,424.80