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 $247.64   13.864%   $281.9728   $281.97   $281.95   $282.00  
  Purchase #2 $78.58   8.856%   $85.539   $85.54   $85.55   $85.50  
  Purchase #3 $195.47   7.607%   $210.3394   $210.34   $210.35   $210.30  
  Purchase #4 $172.73   6.493%   $183.9454   $183.95   $183.95   $183.90  
  Purchase #5 $8.26   4.275%   $8.6131   $8.61   $8.60   $8.60  
  Purchase #6 $86.89   9.660%   $95.2836   $95.28   $95.30   $95.30  
  Purchase #7 $208.47   5.372%   $219.669   $219.67   $219.65   $219.70  
  7 purchase totals = $998.04       $1,085.3623   $1,085.36   $1,085.35   $1,085.30