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	$57.25	13.661%	$65.0709	$65.07	$65.05	$65.10
Purchase #2	$117.48	10.506%	$129.8224	$129.82	$129.80	$129.80
Purchase #3	$204.72	6.286%	$217.5887	$217.59	$217.60	$217.60
Purchase #4	$53.95	12.265%	$60.567	$60.57	$60.55	$60.60
Purchase #5	$158.30	8.463%	$171.6969	$171.70	$171.70	$171.70
Purchase #6	$89.48	12.432%	$100.6042	$100.60	$100.60	$100.60
Purchase #7	$229.29	10.653%	$253.7163	$253.72	$253.70	$253.70
7 purchase totals =	$910.47		$999.0664	$999.07	$999.00	$999.10