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	$117.94	12.321%	$132.4714	$132.47	$132.45	$132.50
Purchase #2	$32.63	6.476%	$34.7431	$34.74	$34.75	$34.70
Purchase #3	$138.86	9.187%	$151.6171	$151.62	$151.60	$151.60
Purchase #4	$25.55	5.740%	$27.0166	$27.02	$27.00	$27.00
Purchase #5	$105.62	6.654%	$112.648	$112.65	$112.65	$112.60
Purchase #6	$29.67	9.463%	$32.4777	$32.48	$32.50	$32.50
Purchase #7	$73.43	12.208%	$82.3943	$82.39	$82.40	$82.40
7 purchase totals =	$523.70		$573.3682	$573.37	$573.35	$573.30