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	$100.58	10.528%	$111.1691	$111.17	$111.15	$111.20
Purchase #2	$158.62	8.577%	$172.2248	$172.22	$172.20	$172.20
Purchase #3	$179.72	6.714%	$191.7864	$191.79	$191.80	$191.80
Purchase #4	$141.31	10.695%	$156.4231	$156.42	$156.40	$156.40
Purchase #5	$79.98	5.621%	$84.4757	$84.48	$84.50	$84.50
Purchase #6	$77.73	9.373%	$85.0156	$85.02	$85.00	$85.00
Purchase #7	$89.66	10.155%	$98.765	$98.77	$98.75	$98.80
7 purchase totals =	$827.60		$899.8597	$899.87	$899.80	$899.90