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	$38.84	4.446%	$40.5668	$40.57	$40.55	$40.60
Purchase #2	$73.85	7.782%	$79.597	$79.60	$79.60	$79.60
Purchase #3	$143.50	8.832%	$156.1739	$156.17	$156.15	$156.20
Purchase #4	$76.78	11.456%	$85.5759	$85.58	$85.60	$85.60
Purchase #5	$99.79	11.698%	$111.4634	$111.46	$111.45	$111.50
Purchase #6	$223.89	13.345%	$253.7681	$253.77	$253.75	$253.80
Purchase #7	$153.89	3.561%	$159.37	$159.37	$159.35	$159.40
7 purchase totals =	$810.54		$886.5151	$886.52	$886.45	$886.70