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	$99.93	8.568%	$108.492	$108.49	$108.50	$108.50
Purchase #2	$162.37	10.391%	$179.2419	$179.24	$179.25	$179.20
Purchase #3	$158.91	8.670%	$172.6875	$172.69	$172.70	$172.70
Purchase #4	$57.41	4.291%	$59.8735	$59.87	$59.85	$59.90
Purchase #5	$55.96	11.834%	$62.5823	$62.58	$62.60	$62.60
Purchase #6	$57.58	4.652%	$60.2586	$60.26	$60.25	$60.30
Purchase #7	$6.61	10.668%	$7.3152	$7.32	$7.30	$7.30
7 purchase totals =	$598.77		$650.4510	$650.45	$650.45	$650.50