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	$123.74	3.490%	$128.0585	$128.06	$128.05	$128.10
Purchase #2	$52.59	3.823%	$54.6005	$54.60	$54.60	$54.60
Purchase #3	$74.94	11.440%	$83.5131	$83.51	$83.50	$83.50
Purchase #4	$124.86	8.565%	$135.5543	$135.55	$135.55	$135.60
Purchase #5	$102.90	7.595%	$110.7153	$110.72	$110.70	$110.70
Purchase #6	$110.30	7.218%	$118.2615	$118.26	$118.25	$118.30
Purchase #7	$102.57	8.513%	$111.3018	$111.30	$111.30	$111.30
7 purchase totals =	$691.90		$742.0050	$742.00	$741.95	$742.10