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	$50.35	6.297%	$53.5205	$53.52	$53.50	$53.50
Purchase #2	$8.69	4.864%	$9.1127	$9.11	$9.10	$9.10
Purchase #3	$27.36	8.801%	$29.768	$29.77	$29.75	$29.80
Purchase #4	$161.51	8.443%	$175.1463	$175.15	$175.15	$175.10
Purchase #5	$10.69	13.667%	$12.151	$12.15	$12.15	$12.20
Purchase #6	$75.30	4.140%	$78.4174	$78.42	$78.40	$78.40
Purchase #7	$59.36	12.501%	$66.7806	$66.78	$66.80	$66.80
7 purchase totals =	$393.26		$424.8965	$424.90	$424.85	$424.90