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	$48.59	11.574%	$54.2138	$54.21	$54.20	$54.20
Purchase #2	$233.78	9.537%	$256.0756	$256.08	$256.10	$256.10
Purchase #3	$223.56	12.468%	$251.4335	$251.43	$251.45	$251.40
Purchase #4	$102.51	8.830%	$111.5616	$111.56	$111.55	$111.60
Purchase #5	$83.48	9.170%	$91.1351	$91.14	$91.15	$91.10
Purchase #6	$177.90	10.742%	$197.01	$197.01	$197.00	$197.00
Purchase #7	$209.47	12.429%	$235.505	$235.51	$235.50	$235.50
7 purchase totals =	$1,079.29		$1,196.9346	$1,196.94	$1,196.95	$1,196.90