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 $176.54   11.183%   $196.2825   $196.28   $196.30   $196.30  
  Purchase #2 $10.46   13.826%   $11.9062   $11.91   $11.90   $11.90  
  Purchase #3 $68.83   11.434%   $76.7   $76.70   $76.70   $76.70  
  Purchase #4 $215.37   9.686%   $236.2307   $236.23   $236.25   $236.20  
  Purchase #5 $179.73   3.409%   $185.857   $185.86   $185.85   $185.90  
  Purchase #6 $61.75   7.540%   $66.406   $66.41   $66.40   $66.40  
  Purchase #7 $115.88   4.428%   $121.0112   $121.01   $121.00   $121.00  
  7 purchase totals = $828.56       $894.3936   $894.40   $894.40   $894.40