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	$132.76	3.786%	$137.7863	$137.79	$137.80	$137.80
Purchase #2	$122.75	4.151%	$127.8454	$127.85	$127.85	$127.80
Purchase #3	$149.44	6.613%	$159.3225	$159.32	$159.30	$159.30
Purchase #4	$49.79	10.696%	$55.1155	$55.12	$55.10	$55.10
Purchase #5	$128.91	10.379%	$142.2896	$142.29	$142.30	$142.30
Purchase #6	$95.91	3.825%	$99.5786	$99.58	$99.60	$99.60
Purchase #7	$224.40	3.758%	$232.833	$232.83	$232.85	$232.80
7 purchase totals =	$903.96		$954.7709	$954.78	$954.80	$954.70