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 $200.50   6.668%   $213.8693   $213.87   $213.85   $213.90  
  Purchase #2 $217.29   7.518%   $233.6259   $233.63   $233.65   $233.60  
  Purchase #3 $112.42   13.108%   $127.156   $127.16   $127.15   $127.20  
  Purchase #4 $232.65   12.726%   $262.257   $262.26   $262.25   $262.30  
  Purchase #5 $233.79   3.597%   $242.1994   $242.20   $242.20   $242.20  
  Purchase #6 $43.68   5.575%   $46.1152   $46.12   $46.10   $46.10  
  Purchase #7 $78.48   4.216%   $81.7887   $81.79   $81.80   $81.80  
  7 purchase totals = $1,118.81       $1,207.0115   $1,207.03   $1,207.00   $1,207.10