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	$107.46	13.472%	$121.937	$121.94	$121.95	$121.90
Purchase #2	$175.66	5.835%	$185.9098	$185.91	$185.90	$185.90
Purchase #3	$6.69	13.155%	$7.5701	$7.57	$7.55	$7.60
Purchase #4	$111.91	11.284%	$124.5379	$124.54	$124.55	$124.50
Purchase #5	$9.50	10.163%	$10.4655	$10.47	$10.45	$10.50
Purchase #6	$205.62	8.142%	$222.3616	$222.36	$222.35	$222.40
Purchase #7	$219.37	10.168%	$241.6755	$241.68	$241.70	$241.70
7 purchase totals =	$836.21		$914.4574	$914.47	$914.45	$914.50