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 $91.89   6.862%   $98.1955   $98.20   $98.20   $98.20  
  Purchase #2 $88.72   4.559%   $92.7647   $92.76   $92.75   $92.80  
  Purchase #3 $206.35   11.272%   $229.6098   $229.61   $229.60   $229.60  
  Purchase #4 $226.33   11.414%   $252.1633   $252.16   $252.15   $252.20  
  Purchase #5 $230.88   11.126%   $256.5677   $256.57   $256.55   $256.60  
  Purchase #6 $248.63   8.159%   $268.9157   $268.92   $268.90   $268.90  
  Purchase #7 $14.33   9.301%   $15.6628   $15.66   $15.65   $15.70  
  7 purchase totals = $1,107.13       $1,213.8795   $1,213.88   $1,213.80   $1,214.00