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	$86.76	3.413%	$89.7211	$89.72	$89.70	$89.70
Purchase #2	$172.38	9.594%	$188.9181	$188.92	$188.90	$188.90
Purchase #3	$208.30	11.826%	$232.9336	$232.93	$232.95	$232.90
Purchase #4	$94.27	5.680%	$99.6245	$99.62	$99.60	$99.60
Purchase #5	$174.74	9.519%	$191.3735	$191.37	$191.35	$191.40
Purchase #6	$101.57	10.496%	$112.2308	$112.23	$112.25	$112.20
Purchase #7	$47.81	10.785%	$52.9663	$52.97	$52.95	$53.00
7 purchase totals =	$885.83		$967.7679	$967.76	$967.70	$967.70