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	$67.38	6.105%	$71.4935	$71.49	$71.50	$71.50
Purchase #2	$55.37	10.247%	$61.0438	$61.04	$61.05	$61.00
Purchase #3	$83.76	7.381%	$89.9423	$89.94	$89.95	$89.90
Purchase #4	$231.36	4.734%	$242.3126	$242.31	$242.30	$242.30
Purchase #5	$22.37	10.320%	$24.6786	$24.68	$24.70	$24.70
Purchase #6	$158.43	9.387%	$173.3018	$173.30	$173.30	$173.30
Purchase #7	$180.51	7.231%	$193.5627	$193.56	$193.55	$193.60
7 purchase totals =	$799.18		$856.3353	$856.32	$856.35	$856.30