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 $56.66   3.433%   $58.6051   $58.61   $58.60   $58.60  
  Purchase #2 $52.34   4.660%   $54.779   $54.78   $54.80   $54.80  
  Purchase #3 $206.47   3.641%   $213.9876   $213.99   $214.00   $214.00  
  Purchase #4 $82.25   3.720%   $85.3097   $85.31   $85.30   $85.30  
  Purchase #5 $151.75   4.262%   $158.2176   $158.22   $158.20   $158.20  
  Purchase #6 $232.59   3.769%   $241.3563   $241.36   $241.35   $241.40  
  Purchase #7 $52.31   10.191%   $57.6409   $57.64   $57.65   $57.60  
  7 purchase totals = $834.37       $869.8962   $869.91   $869.90   $869.90