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	$46.65	6.518%	$49.6906	$49.69	$49.70	$49.70
Purchase #2	$24.89	4.264%	$25.9513	$25.95	$25.95	$26.00
Purchase #3	$92.69	7.377%	$99.5277	$99.53	$99.55	$99.50
Purchase #4	$50.81	5.331%	$53.5187	$53.52	$53.50	$53.50
Purchase #5	$58.93	12.752%	$66.4448	$66.44	$66.45	$66.40
Purchase #6	$71.27	9.297%	$77.896	$77.90	$77.90	$77.90
Purchase #7	$235.76	13.124%	$266.7011	$266.70	$266.70	$266.70
7 purchase totals =	$581.00		$639.7302	$639.73	$639.75	$639.70