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 $224.81   9.446%   $246.0456   $246.05   $246.05   $246.00  
  Purchase #2 $137.74   9.287%   $150.5319   $150.53   $150.55   $150.50  
  Purchase #3 $114.75   3.399%   $118.6504   $118.65   $118.65   $118.70  
  Purchase #4 $147.88   3.503%   $153.0602   $153.06   $153.05   $153.10  
  Purchase #5 $137.35   10.493%   $151.7621   $151.76   $151.75   $151.80  
  Purchase #6 $208.26   12.673%   $234.6528   $234.65   $234.65   $234.70  
  Purchase #7 $178.80   12.104%   $200.442   $200.44   $200.45   $200.40  
  7 purchase totals = $1,149.59       $1,255.1450   $1,255.14   $1,255.15   $1,255.20