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	$214.48	11.325%	$238.7699	$238.77	$238.75	$238.80
Purchase #2	$153.56	7.302%	$164.773	$164.77	$164.75	$164.80
Purchase #3	$10.75	13.648%	$12.2172	$12.22	$12.20	$12.20
Purchase #4	$238.63	6.655%	$254.5108	$254.51	$254.50	$254.50
Purchase #5	$52.96	3.178%	$54.6431	$54.64	$54.65	$54.60
Purchase #6	$73.67	9.618%	$80.7556	$80.76	$80.75	$80.80
Purchase #7	$178.32	5.160%	$187.5213	$187.52	$187.50	$187.50
7 purchase totals =	$922.37		$993.1909	$993.19	$993.10	$993.20