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	$86.88	11.765%	$97.1014	$97.10	$97.10	$97.10
Purchase #2	$97.45	3.179%	$100.5479	$100.55	$100.55	$100.50
Purchase #3	$47.73	8.771%	$51.9164	$51.92	$51.90	$51.90
Purchase #4	$60.34	10.658%	$66.771	$66.77	$66.75	$66.80
Purchase #5	$81.63	10.605%	$90.2869	$90.29	$90.30	$90.30
Purchase #6	$206.70	11.589%	$230.6545	$230.65	$230.65	$230.70
Purchase #7	$46.65	4.244%	$48.6298	$48.63	$48.65	$48.60
7 purchase totals =	$627.38		$685.9079	$685.91	$685.90	$685.90