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 $224.58   10.404%   $247.9453   $247.95   $247.95   $247.90  
  Purchase #2 $104.99   8.703%   $114.1273   $114.13   $114.15   $114.10  
  Purchase #3 $23.88   5.276%   $25.1399   $25.14   $25.15   $25.10  
  Purchase #4 $242.43   9.859%   $266.3312   $266.33   $266.35   $266.30  
  Purchase #5 $160.46   10.664%   $177.5715   $177.57   $177.55   $177.60  
  Purchase #6 $153.88   9.145%   $167.9523   $167.95   $167.95   $168.00  
  Purchase #7 $248.99   7.365%   $267.3281   $267.33   $267.35   $267.30  
  7 purchase totals = $1,159.21       $1,266.3956   $1,266.40   $1,266.45   $1,266.30