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 $216.93   13.805%   $246.8772   $246.88   $246.90   $246.90  
  Purchase #2 $26.44   11.120%   $29.3801   $29.38   $29.40   $29.40  
  Purchase #3 $175.77   4.261%   $183.2596   $183.26   $183.25   $183.30  
  Purchase #4 $190.41   9.503%   $208.5047   $208.50   $208.50   $208.50  
  Purchase #5 $146.59   8.469%   $159.0047   $159.00   $159.00   $159.00  
  Purchase #6 $141.88   11.855%   $158.6999   $158.70   $158.70   $158.70  
  Purchase #7 $195.63   7.639%   $210.5742   $210.57   $210.55   $210.60  
  7 purchase totals = $1,093.65       $1,196.3004   $1,196.29   $1,196.30   $1,196.40