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	$211.74	8.227%	$229.1598	$229.16	$229.15	$229.20
Purchase #2	$54.89	13.872%	$62.5043	$62.50	$62.50	$62.50
Purchase #3	$50.73	11.170%	$56.3965	$56.40	$56.40	$56.40
Purchase #4	$197.87	8.562%	$214.8116	$214.81	$214.80	$214.80
Purchase #5	$71.93	12.545%	$80.9536	$80.95	$80.95	$81.00
Purchase #6	$226.53	13.253%	$256.552	$256.55	$256.55	$256.60
Purchase #7	$84.41	6.532%	$89.9237	$89.92	$89.90	$89.90
7 purchase totals =	$898.10		$990.3015	$990.29	$990.25	$990.40