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 $60.53   10.181%   $66.6926   $66.69   $66.70   $66.70  
  Purchase #2 $215.50   13.515%   $244.6248   $244.62   $244.60   $244.60  
  Purchase #3 $166.49   13.352%   $188.7197   $188.72   $188.70   $188.70  
  Purchase #4 $186.51   3.403%   $192.8569   $192.86   $192.85   $192.90  
  Purchase #5 $162.99   4.141%   $169.7394   $169.74   $169.75   $169.70  
  Purchase #6 $48.62   8.623%   $52.8125   $52.81   $52.80   $52.80  
  Purchase #7 $227.64   5.182%   $239.4363   $239.44   $239.45   $239.40  
  7 purchase totals = $1,068.28       $1,154.8822   $1,154.88   $1,154.85   $1,154.80