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 $59.63   6.777%   $63.6711   $63.67   $63.65   $63.70  
  Purchase #2 $69.41   6.269%   $73.7613   $73.76   $73.75   $73.80  
  Purchase #3 $96.37   12.700%   $108.609   $108.61   $108.60   $108.60  
  Purchase #4 $96.71   4.874%   $101.4236   $101.42   $101.40   $101.40  
  Purchase #5 $88.57   10.550%   $97.9141   $97.91   $97.90   $97.90  
  Purchase #6 $192.59   3.642%   $199.6041   $199.60   $199.60   $199.60  
  Purchase #7 $75.83   8.139%   $82.0018   $82.00   $82.00   $82.00  
  7 purchase totals = $679.11       $726.9850   $726.97   $726.90   $727.00