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	$121.87	12.826%	$137.501	$137.50	$137.50	$137.50
Purchase #2	$129.25	9.845%	$141.9747	$141.97	$141.95	$142.00
Purchase #3	$174.50	10.788%	$193.3251	$193.33	$193.35	$193.30
Purchase #4	$28.74	11.519%	$32.0506	$32.05	$32.05	$32.10
Purchase #5	$153.38	12.469%	$172.505	$172.51	$172.50	$172.50
Purchase #6	$105.79	5.747%	$111.8698	$111.87	$111.85	$111.90
Purchase #7	$174.41	11.130%	$193.8218	$193.82	$193.80	$193.80
7 purchase totals =	$887.94		$983.0480	$983.05	$983.00	$983.10