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	$46.88	9.325%	$51.2516	$51.25	$51.25	$51.30
Purchase #2	$14.62	7.693%	$15.7447	$15.74	$15.75	$15.70
Purchase #3	$83.40	9.727%	$91.5123	$91.51	$91.50	$91.50
Purchase #4	$81.83	9.700%	$89.7675	$89.77	$89.75	$89.80
Purchase #5	$146.91	3.809%	$152.5058	$152.51	$152.50	$152.50
Purchase #6	$50.54	13.324%	$57.2739	$57.27	$57.25	$57.30
Purchase #7	$84.75	5.710%	$89.5892	$89.59	$89.60	$89.60
7 purchase totals =	$508.93		$547.6450	$547.64	$547.60	$547.70