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 $249.63   10.322%   $275.3968   $275.40   $275.40   $275.40  
  Purchase #2 $136.74   6.314%   $145.3738   $145.37   $145.35   $145.40  
  Purchase #3 $209.45   5.534%   $221.041   $221.04   $221.05   $221.00  
  Purchase #4 $38.99   11.726%   $43.562   $43.56   $43.55   $43.60  
  Purchase #5 $95.99   12.120%   $107.624   $107.62   $107.60   $107.60  
  Purchase #6 $57.86   7.847%   $62.4003   $62.40   $62.40   $62.40  
  Purchase #7 $241.36   3.388%   $249.5373   $249.54   $249.55   $249.50  
  7 purchase totals = $1,030.02       $1,104.9352   $1,104.93   $1,104.90   $1,104.90