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 $200.97   6.618%   $214.2702   $214.27   $214.25   $214.30  
  Purchase #2 $78.73   7.443%   $84.5899   $84.59   $84.60   $84.60  
  Purchase #3 $109.59   13.788%   $124.7003   $124.70   $124.70   $124.70  
  Purchase #4 $116.66   6.694%   $124.4692   $124.47   $124.45   $124.50  
  Purchase #5 $184.54   5.242%   $194.2136   $194.21   $194.20   $194.20  
  Purchase #6 $22.78   3.538%   $23.586   $23.59   $23.60   $23.60  
  Purchase #7 $62.91   9.205%   $68.7009   $68.70   $68.70   $68.70  
  7 purchase totals = $776.18       $834.5301   $834.53   $834.50   $834.60