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	$163.97	12.111%	$183.8284	$183.83	$183.85	$183.80
Purchase #2	$61.59	7.392%	$66.1427	$66.14	$66.15	$66.10
Purchase #3	$142.91	10.275%	$157.594	$157.59	$157.60	$157.60
Purchase #4	$128.55	13.490%	$145.8914	$145.89	$145.90	$145.90
Purchase #5	$90.76	10.837%	$100.5957	$100.60	$100.60	$100.60
Purchase #6	$230.61	11.718%	$257.6329	$257.63	$257.65	$257.60
Purchase #7	$12.56	7.286%	$13.4751	$13.48	$13.50	$13.50
7 purchase totals =	$830.95		$925.1602	$925.16	$925.25	$925.10