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	$153.66	10.304%	$169.4931	$169.49	$169.50	$169.50
Purchase #2	$176.58	4.636%	$184.7662	$184.77	$184.75	$184.80
Purchase #3	$108.25	11.332%	$120.5169	$120.52	$120.50	$120.50
Purchase #4	$73.44	6.345%	$78.0998	$78.10	$78.10	$78.10
Purchase #5	$37.45	9.181%	$40.8883	$40.89	$40.90	$40.90
Purchase #6	$69.48	12.242%	$77.9857	$77.99	$78.00	$78.00
Purchase #7	$63.46	13.473%	$72.01	$72.01	$72.00	$72.00
7 purchase totals =	$682.32		$743.7600	$743.77	$743.75	$743.80