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	$122.91	11.861%	$137.4884	$137.49	$137.50	$137.50
Purchase #2	$124.39	6.421%	$132.3771	$132.38	$132.40	$132.40
Purchase #3	$240.50	10.662%	$266.1421	$266.14	$266.15	$266.10
Purchase #4	$165.45	8.679%	$179.8094	$179.81	$179.80	$179.80
Purchase #5	$46.36	10.286%	$51.1286	$51.13	$51.15	$51.10
Purchase #6	$220.51	12.697%	$248.5082	$248.51	$248.50	$248.50
Purchase #7	$99.80	5.732%	$105.5205	$105.52	$105.50	$105.50
7 purchase totals =	$1,019.92		$1,120.9743	$1,120.98	$1,121.00	$1,120.90