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	$104.64	7.513%	$112.5016	$112.50	$112.50	$112.50
Purchase #2	$19.72	11.485%	$21.9848	$21.98	$22.00	$22.00
Purchase #3	$141.60	12.527%	$159.3382	$159.34	$159.35	$159.30
Purchase #4	$90.85	9.534%	$99.5116	$99.51	$99.50	$99.50
Purchase #5	$113.42	11.663%	$126.6482	$126.65	$126.65	$126.60
Purchase #6	$170.67	11.401%	$190.1281	$190.13	$190.15	$190.10
Purchase #7	$230.28	13.608%	$261.6165	$261.62	$261.60	$261.60
7 purchase totals =	$871.18		$971.7290	$971.73	$971.75	$971.60