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	$19.56	12.246%	$21.9553	$21.96	$21.95	$22.00
Purchase #2	$36.51	6.178%	$38.7656	$38.77	$38.75	$38.80
Purchase #3	$10.25	4.495%	$10.7107	$10.71	$10.70	$10.70
Purchase #4	$61.67	7.753%	$66.4513	$66.45	$66.45	$66.50
Purchase #5	$188.82	6.206%	$200.5382	$200.54	$200.55	$200.50
Purchase #6	$81.85	11.661%	$91.3945	$91.39	$91.40	$91.40
Purchase #7	$31.82	4.616%	$33.2888	$33.29	$33.30	$33.30
7 purchase totals =	$430.48		$463.1044	$463.11	$463.10	$463.20