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	$212.93	13.781%	$242.2739	$242.27	$242.25	$242.30
Purchase #2	$243.53	9.524%	$266.7238	$266.72	$266.70	$266.70
Purchase #3	$46.89	13.505%	$53.2225	$53.22	$53.20	$53.20
Purchase #4	$9.62	12.829%	$10.8541	$10.85	$10.85	$10.90
Purchase #5	$70.94	10.496%	$78.3859	$78.39	$78.40	$78.40
Purchase #6	$52.95	7.626%	$56.988	$56.99	$57.00	$57.00
Purchase #7	$116.53	9.559%	$127.6691	$127.67	$127.65	$127.70
7 purchase totals =	$753.39		$836.1173	$836.11	$836.05	$836.20