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 $238.99   9.739%   $262.2652   $262.27   $262.25   $262.30  
  Purchase #2 $138.26   11.591%   $154.2857   $154.29   $154.30   $154.30  
  Purchase #3 $245.63   11.343%   $273.4918   $273.49   $273.50   $273.50  
  Purchase #4 $55.90   8.186%   $60.476   $60.48   $60.50   $60.50  
  Purchase #5 $228.61   7.501%   $245.758   $245.76   $245.75   $245.80  
  Purchase #6 $198.33   4.386%   $207.0288   $207.03   $207.05   $207.00  
  Purchase #7 $7.95   13.663%   $9.0362   $9.04   $9.05   $9.00  
  7 purchase totals = $1,113.67       $1,212.3417   $1,212.36   $1,212.40   $1,212.40