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	$228.98	9.390%	$250.4812	$250.48	$250.50	$250.50
Purchase #2	$54.40	4.275%	$56.7256	$56.73	$56.75	$56.70
Purchase #3	$96.81	13.479%	$109.859	$109.86	$109.85	$109.90
Purchase #4	$91.48	11.862%	$102.3314	$102.33	$102.35	$102.30
Purchase #5	$32.31	3.217%	$33.3494	$33.35	$33.35	$33.30
Purchase #6	$74.70	10.688%	$82.6839	$82.68	$82.70	$82.70
Purchase #7	$111.84	13.766%	$127.2359	$127.24	$127.25	$127.20
7 purchase totals =	$690.52		$762.6664	$762.67	$762.75	$762.60