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	$108.57	12.589%	$122.2379	$122.24	$122.25	$122.20
Purchase #2	$209.94	7.384%	$225.442	$225.44	$225.45	$225.40
Purchase #3	$10.47	8.748%	$11.3859	$11.39	$11.40	$11.40
Purchase #4	$63.72	11.678%	$71.1612	$71.16	$71.15	$71.20
Purchase #5	$199.37	4.635%	$208.6108	$208.61	$208.60	$208.60
Purchase #6	$44.94	11.510%	$50.1126	$50.11	$50.10	$50.10
Purchase #7	$204.83	8.814%	$222.8837	$222.88	$222.90	$222.90
7 purchase totals =	$841.84		$911.8341	$911.83	$911.85	$911.80