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 $68.59   12.848%   $77.4024   $77.40   $77.40   $77.40  
  Purchase #2 $107.72   9.184%   $117.613   $117.61   $117.60   $117.60  
  Purchase #3 $25.68   6.579%   $27.3695   $27.37   $27.35   $27.40  
  Purchase #4 $32.28   5.291%   $33.9879   $33.99   $34.00   $34.00  
  Purchase #5 $83.85   10.832%   $92.9326   $92.93   $92.95   $92.90  
  Purchase #6 $240.99   8.863%   $262.3489   $262.35   $262.35   $262.30  
  Purchase #7 $128.59   9.199%   $140.419   $140.42   $140.40   $140.40  
  7 purchase totals = $687.70       $752.0733   $752.07   $752.05   $752.00