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	$210.28	13.324%	$238.2977	$238.30	$238.30	$238.30
Purchase #2	$69.78	6.669%	$74.4336	$74.43	$74.45	$74.40
Purchase #3	$65.54	11.764%	$73.2501	$73.25	$73.25	$73.30
Purchase #4	$47.35	10.706%	$52.4193	$52.42	$52.40	$52.40
Purchase #5	$164.71	4.751%	$172.5354	$172.54	$172.55	$172.50
Purchase #6	$32.69	13.437%	$37.0826	$37.08	$37.10	$37.10
Purchase #7	$9.39	6.682%	$10.0174	$10.02	$10.00	$10.00
7 purchase totals =	$599.74		$658.0361	$658.04	$658.05	$658.00