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	$111.36	12.146%	$124.8858	$124.89	$124.90	$124.90
Purchase #2	$85.60	3.812%	$88.8631	$88.86	$88.85	$88.90
Purchase #3	$117.46	8.204%	$127.0964	$127.10	$127.10	$127.10
Purchase #4	$20.73	3.221%	$21.3977	$21.40	$21.40	$21.40
Purchase #5	$55.38	9.530%	$60.6577	$60.66	$60.65	$60.70
Purchase #6	$210.41	3.207%	$217.1578	$217.16	$217.15	$217.20
Purchase #7	$151.69	7.201%	$162.6132	$162.61	$162.60	$162.60
7 purchase totals =	$752.63		$802.6717	$802.68	$802.65	$802.80