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 $214.66   3.276%   $221.6923   $221.69   $221.70   $221.70  
  Purchase #2 $207.92   7.113%   $222.7093   $222.71   $222.70   $222.70  
  Purchase #3 $84.28   12.130%   $94.5032   $94.50   $94.50   $94.50  
  Purchase #4 $150.59   5.475%   $158.8348   $158.83   $158.85   $158.80  
  Purchase #5 $165.37   12.238%   $185.608   $185.61   $185.60   $185.60  
  Purchase #6 $209.26   11.262%   $232.8269   $232.83   $232.85   $232.80  
  Purchase #7 $107.91   12.679%   $121.5919   $121.59   $121.60   $121.60  
  7 purchase totals = $1,139.99       $1,237.7664   $1,237.76   $1,237.80   $1,237.70