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	$172.26	8.616%	$187.1019	$187.10	$187.10	$187.10
Purchase #2	$141.44	11.820%	$158.1582	$158.16	$158.15	$158.20
Purchase #3	$95.25	5.262%	$100.2621	$100.26	$100.25	$100.30
Purchase #4	$100.63	3.252%	$103.9025	$103.90	$103.90	$103.90
Purchase #5	$162.53	9.318%	$177.6745	$177.67	$177.65	$177.70
Purchase #6	$223.70	6.607%	$238.4799	$238.48	$238.50	$238.50
Purchase #7	$92.90	7.734%	$100.0849	$100.08	$100.10	$100.10
7 purchase totals =	$988.71		$1,065.6640	$1,065.65	$1,065.65	$1,065.80