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	$18.73	10.437%	$20.6849	$20.68	$20.70	$20.70
Purchase #2	$154.63	12.145%	$173.4098	$173.41	$173.40	$173.40
Purchase #3	$89.86	11.227%	$99.9486	$99.95	$99.95	$99.90
Purchase #4	$228.30	13.574%	$259.2894	$259.29	$259.30	$259.30
Purchase #5	$206.68	13.162%	$233.8832	$233.88	$233.90	$233.90
Purchase #6	$231.49	3.171%	$238.8305	$238.83	$238.85	$238.80
Purchase #7	$160.37	8.203%	$173.5252	$173.53	$173.55	$173.50
7 purchase totals =	$1,090.06		$1,199.5716	$1,199.57	$1,199.65	$1,199.50