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	$37.42	13.638%	$42.5233	$42.52	$42.50	$42.50
Purchase #2	$190.76	12.573%	$214.7443	$214.74	$214.75	$214.70
Purchase #3	$232.49	11.251%	$258.6474	$258.65	$258.65	$258.60
Purchase #4	$156.48	6.698%	$166.961	$166.96	$166.95	$167.00
Purchase #5	$129.41	10.277%	$142.7095	$142.71	$142.70	$142.70
Purchase #6	$83.94	10.826%	$93.0273	$93.03	$93.05	$93.00
Purchase #7	$86.82	4.125%	$90.4013	$90.40	$90.40	$90.40
7 purchase totals =	$917.32		$1,009.0141	$1,009.01	$1,009.00	$1,008.90