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 $17.31   10.175%   $19.0713   $19.07   $19.05   $19.10  
  Purchase #2 $240.37   3.233%   $248.1412   $248.14   $248.15   $248.10  
  Purchase #3 $17.90   9.607%   $19.6197   $19.62   $19.60   $19.60  
  Purchase #4 $146.69   3.489%   $151.808   $151.81   $151.80   $151.80  
  Purchase #5 $128.59   8.639%   $139.6989   $139.70   $139.70   $139.70  
  Purchase #6 $149.38   6.632%   $159.2869   $159.29   $159.30   $159.30  
  Purchase #7 $227.63   6.250%   $241.8569   $241.86   $241.85   $241.90  
  7 purchase totals = $927.87       $979.4829   $979.49   $979.45   $979.50