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	$158.49	8.614%	$172.1423	$172.14	$172.15	$172.10
Purchase #2	$80.73	3.778%	$83.78	$83.78	$83.80	$83.80
Purchase #3	$168.96	3.685%	$175.1862	$175.19	$175.20	$175.20
Purchase #4	$229.40	6.706%	$244.7836	$244.78	$244.80	$244.80
Purchase #5	$229.43	6.153%	$243.5468	$243.55	$243.55	$243.50
Purchase #6	$44.71	13.123%	$50.5773	$50.58	$50.60	$50.60
Purchase #7	$21.42	5.233%	$22.5409	$22.54	$22.55	$22.50
7 purchase totals =	$933.14		$992.5571	$992.56	$992.65	$992.50