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	$155.76	10.760%	$172.5198	$172.52	$172.50	$172.50
Purchase #2	$94.90	4.533%	$99.2018	$99.20	$99.20	$99.20
Purchase #3	$78.39	10.183%	$86.3725	$86.37	$86.35	$86.40
Purchase #4	$214.35	7.867%	$231.2129	$231.21	$231.20	$231.20
Purchase #5	$122.36	4.595%	$127.9824	$127.98	$128.00	$128.00
Purchase #6	$12.89	13.651%	$14.6496	$14.65	$14.65	$14.60
Purchase #7	$238.28	8.626%	$258.834	$258.83	$258.85	$258.80
7 purchase totals =	$916.93		$990.7730	$990.76	$990.75	$990.70