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 $249.56   6.285%   $265.2448   $265.24   $265.25   $265.20  
  Purchase #2 $86.38   11.266%   $96.1116   $96.11   $96.10   $96.10  
  Purchase #3 $39.43   13.716%   $44.8382   $44.84   $44.85   $44.80  
  Purchase #4 $38.28   4.571%   $40.0298   $40.03   $40.05   $40.00  
  Purchase #5 $84.41   11.475%   $94.096   $94.10   $94.10   $94.10  
  Purchase #6 $163.41   3.420%   $168.9986   $169.00   $169.00   $169.00  
  Purchase #7 $165.70   7.653%   $178.381   $178.38   $178.40   $178.40  
  7 purchase totals = $827.17       $887.7000   $887.70   $887.75   $887.60