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	$134.36	12.845%	$151.6185	$151.62	$151.60	$151.60
Purchase #2	$168.32	3.839%	$174.7818	$174.78	$174.80	$174.80
Purchase #3	$184.71	11.545%	$206.0348	$206.03	$206.05	$206.00
Purchase #4	$230.89	6.736%	$246.4428	$246.44	$246.45	$246.40
Purchase #5	$49.83	4.158%	$51.9019	$51.90	$51.90	$51.90
Purchase #6	$89.73	10.472%	$99.1265	$99.13	$99.15	$99.10
Purchase #7	$56.64	6.827%	$60.5068	$60.51	$60.50	$60.50
7 purchase totals =	$914.48		$990.4131	$990.41	$990.45	$990.30