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 $219.95   5.664%   $232.408   $232.41   $232.40   $232.40  
  Purchase #2 $177.38   12.241%   $199.0931   $199.09   $199.10   $199.10  
  Purchase #3 $41.27   11.233%   $45.9059   $45.91   $45.90   $45.90  
  Purchase #4 $62.83   10.238%   $69.2625   $69.26   $69.25   $69.30  
  Purchase #5 $67.29   9.416%   $73.626   $73.63   $73.65   $73.60  
  Purchase #6 $167.44   10.510%   $185.0379   $185.04   $185.05   $185.00  
  Purchase #7 $200.71   11.460%   $223.7114   $223.71   $223.70   $223.70  
  7 purchase totals = $936.87       $1,029.0448   $1,029.05   $1,029.05   $1,029.00