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 $169.68   4.720%   $177.6889   $177.69   $177.70   $177.70  
  Purchase #2 $238.97   13.669%   $271.6348   $271.63   $271.65   $271.60  
  Purchase #3 $79.74   6.463%   $84.8936   $84.89   $84.90   $84.90  
  Purchase #4 $213.99   7.311%   $229.6348   $229.63   $229.65   $229.60  
  Purchase #5 $136.36   6.713%   $145.5138   $145.51   $145.50   $145.50  
  Purchase #6 $249.31   13.272%   $282.3984   $282.40   $282.40   $282.40  
  Purchase #7 $169.50   13.554%   $192.474   $192.47   $192.45   $192.50  
  7 purchase totals = $1,257.55       $1,384.2383   $1,384.22   $1,384.25   $1,384.20