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	$114.55	12.121%	$128.4346	$128.43	$128.45	$128.40
Purchase #2	$219.74	8.344%	$238.0751	$238.08	$238.10	$238.10
Purchase #3	$210.58	9.353%	$230.2755	$230.28	$230.30	$230.30
Purchase #4	$48.77	5.433%	$51.4197	$51.42	$51.40	$51.40
Purchase #5	$35.79	8.495%	$38.8304	$38.83	$38.85	$38.80
Purchase #6	$92.79	7.282%	$99.547	$99.55	$99.55	$99.50
Purchase #7	$95.87	4.758%	$100.4315	$100.43	$100.45	$100.40
7 purchase totals =	$818.09		$887.0138	$887.02	$887.10	$886.90