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 $53.96   11.267%   $60.0397   $60.04   $60.05   $60.00  
  Purchase #2 $213.42   9.160%   $232.9693   $232.97   $232.95   $233.00  
  Purchase #3 $234.86   9.307%   $256.7184   $256.72   $256.70   $256.70  
  Purchase #4 $64.72   7.864%   $69.8096   $69.81   $69.80   $69.80  
  Purchase #5 $194.38   7.318%   $208.6047   $208.60   $208.60   $208.60  
  Purchase #6 $78.89   9.408%   $86.312   $86.31   $86.30   $86.30  
  Purchase #7 $176.87   7.655%   $190.4094   $190.41   $190.40   $190.40  
  7 purchase totals = $1,017.10       $1,104.8631   $1,104.86   $1,104.80   $1,104.80