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	$77.72	7.415%	$83.4829	$83.48	$83.50	$83.50
Purchase #2	$164.76	4.580%	$172.306	$172.31	$172.30	$172.30
Purchase #3	$62.87	9.211%	$68.661	$68.66	$68.65	$68.70
Purchase #4	$28.64	11.505%	$31.935	$31.94	$31.95	$31.90
Purchase #5	$95.75	10.687%	$105.9828	$105.98	$106.00	$106.00
Purchase #6	$59.42	3.186%	$61.3131	$61.31	$61.30	$61.30
Purchase #7	$108.40	8.585%	$117.7061	$117.71	$117.70	$117.70
7 purchase totals =	$597.56		$641.3869	$641.39	$641.40	$641.40