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 $113.95   11.411%   $126.9528   $126.95   $126.95   $127.00  
  Purchase #2 $189.46   6.858%   $202.4532   $202.45   $202.45   $202.50  
  Purchase #3 $22.77   9.462%   $24.9245   $24.92   $24.90   $24.90  
  Purchase #4 $238.96   4.725%   $250.2509   $250.25   $250.25   $250.30  
  Purchase #5 $123.38   8.414%   $133.7612   $133.76   $133.75   $133.80  
  Purchase #6 $114.43   11.555%   $127.6524   $127.65   $127.65   $127.70  
  Purchase #7 $171.64   6.231%   $182.3349   $182.33   $182.35   $182.30  
  7 purchase totals = $974.59       $1,048.3299   $1,048.31   $1,048.30   $1,048.50