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 $22.61   8.836%   $24.6078   $24.61   $24.60   $24.60  
  Purchase #2 $182.47   3.541%   $188.9313   $188.93   $188.95   $188.90  
  Purchase #3 $205.58   4.868%   $215.5876   $215.59   $215.60   $215.60  
  Purchase #4 $230.74   3.676%   $239.222   $239.22   $239.20   $239.20  
  Purchase #5 $29.91   5.337%   $31.5063   $31.51   $31.50   $31.50  
  Purchase #6 $142.36   8.425%   $154.3538   $154.35   $154.35   $154.40  
  Purchase #7 $72.74   10.446%   $80.3384   $80.34   $80.35   $80.30  
  7 purchase totals = $886.41       $934.5472   $934.55   $934.55   $934.50