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	$114.94	8.277%	$124.4536	$124.45	$124.45	$124.50
Purchase #2	$97.85	12.429%	$110.0118	$110.01	$110.00	$110.00
Purchase #3	$159.40	8.300%	$172.6302	$172.63	$172.65	$172.60
Purchase #4	$227.63	11.337%	$253.4364	$253.44	$253.45	$253.40
Purchase #5	$76.82	11.741%	$85.8394	$85.84	$85.85	$85.80
Purchase #6	$103.31	5.816%	$109.3185	$109.32	$109.30	$109.30
Purchase #7	$12.66	13.726%	$14.3977	$14.40	$14.40	$14.40
7 purchase totals =	$792.61		$870.0876	$870.09	$870.10	$870.00