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 $223.66   11.335%   $249.0119   $249.01   $249.00   $249.00  
  Purchase #2 $54.77   10.565%   $60.5565   $60.56   $60.55   $60.60  
  Purchase #3 $63.49   12.323%   $71.3139   $71.31   $71.30   $71.30  
  Purchase #4 $192.51   10.872%   $213.4397   $213.44   $213.45   $213.40  
  Purchase #5 $215.58   8.139%   $233.1261   $233.13   $233.15   $233.10  
  Purchase #6 $61.89   11.473%   $68.9906   $68.99   $69.00   $69.00  
  Purchase #7 $200.62   10.615%   $221.9158   $221.92   $221.90   $221.90  
  7 purchase totals = $1,012.52       $1,118.3545   $1,118.36   $1,118.35   $1,118.30