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 $207.41   10.623%   $229.4432   $229.44   $229.45   $229.40  
  Purchase #2 $92.29   3.320%   $95.354   $95.35   $95.35   $95.40  
  Purchase #3 $130.29   8.189%   $140.9594   $140.96   $140.95   $141.00  
  Purchase #4 $27.56   11.640%   $30.768   $30.77   $30.75   $30.80  
  Purchase #5 $175.86   13.323%   $199.2898   $199.29   $199.30   $199.30  
  Purchase #6 $125.27   4.492%   $130.8971   $130.90   $130.90   $130.90  
  Purchase #7 $175.36   11.372%   $195.3019   $195.30   $195.30   $195.30  
  7 purchase totals = $934.04       $1,022.0134   $1,022.01   $1,022.00   $1,022.10