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	$128.27	7.496%	$137.8851	$137.89	$137.90	$137.90
Purchase #2	$106.89	8.231%	$115.6881	$115.69	$115.70	$115.70
Purchase #3	$149.93	11.220%	$166.7521	$166.75	$166.75	$166.80
Purchase #4	$211.49	10.416%	$233.5188	$233.52	$233.50	$233.50
Purchase #5	$89.76	11.240%	$99.849	$99.85	$99.85	$99.80
Purchase #6	$19.61	6.308%	$20.847	$20.85	$20.85	$20.80
Purchase #7	$132.43	3.741%	$137.3842	$137.38	$137.40	$137.40
7 purchase totals =	$838.38		$911.9243	$911.93	$911.95	$911.90