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 $241.69   3.714%   $250.6664   $250.67   $250.65   $250.70  
  Purchase #2 $40.55   13.781%   $46.1382   $46.14   $46.15   $46.10  
  Purchase #3 $187.65   4.248%   $195.6214   $195.62   $195.60   $195.60  
  Purchase #4 $56.94   11.130%   $63.2774   $63.28   $63.30   $63.30  
  Purchase #5 $162.44   12.436%   $182.641   $182.64   $182.65   $182.60  
  Purchase #6 $248.99   3.717%   $258.245   $258.25   $258.25   $258.20  
  Purchase #7 $140.82   10.707%   $155.8976   $155.90   $155.90   $155.90  
  7 purchase totals = $1,079.08       $1,152.4870   $1,152.50   $1,152.50   $1,152.40