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	$124.85	5.201%	$131.3434	$131.34	$131.35	$131.30
Purchase #2	$152.68	13.205%	$172.8414	$172.84	$172.85	$172.80
Purchase #3	$212.41	6.843%	$226.9452	$226.95	$226.95	$226.90
Purchase #4	$237.59	4.203%	$247.5759	$247.58	$247.60	$247.60
Purchase #5	$131.81	9.710%	$144.6088	$144.61	$144.60	$144.60
Purchase #6	$105.63	5.776%	$111.7312	$111.73	$111.75	$111.70
Purchase #7	$239.93	9.733%	$263.2824	$263.28	$263.30	$263.30
7 purchase totals =	$1,204.90		$1,298.3283	$1,298.33	$1,298.40	$1,298.20