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	$80.99	5.650%	$85.5659	$85.57	$85.55	$85.60
Purchase #2	$53.95	11.667%	$60.2443	$60.24	$60.25	$60.20
Purchase #3	$81.79	9.759%	$89.7719	$89.77	$89.75	$89.80
Purchase #4	$88.65	12.434%	$99.6727	$99.67	$99.65	$99.70
Purchase #5	$20.70	10.138%	$22.7986	$22.80	$22.80	$22.80
Purchase #6	$147.30	7.731%	$158.6878	$158.69	$158.70	$158.70
Purchase #7	$50.80	6.631%	$54.1685	$54.17	$54.15	$54.20
7 purchase totals =	$524.18		$570.9097	$570.91	$570.85	$571.00