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	$60.28	10.251%	$66.4593	$66.46	$66.45	$66.50
Purchase #2	$121.89	5.172%	$128.1942	$128.19	$128.20	$128.20
Purchase #3	$57.51	6.851%	$61.45	$61.45	$61.45	$61.50
Purchase #4	$55.82	10.766%	$61.8296	$61.83	$61.85	$61.80
Purchase #5	$99.91	9.798%	$109.6992	$109.70	$109.70	$109.70
Purchase #6	$188.49	9.282%	$205.9856	$205.99	$206.00	$206.00
Purchase #7	$66.72	9.149%	$72.8242	$72.82	$72.80	$72.80
7 purchase totals =	$650.62		$706.4421	$706.44	$706.45	$706.50