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	$14.68	5.436%	$15.478	$15.48	$15.50	$15.50
Purchase #2	$162.80	5.499%	$171.7524	$171.75	$171.75	$171.80
Purchase #3	$104.84	6.123%	$111.2594	$111.26	$111.25	$111.30
Purchase #4	$40.41	4.734%	$42.323	$42.32	$42.30	$42.30
Purchase #5	$225.42	7.161%	$241.5623	$241.56	$241.55	$241.60
Purchase #6	$102.56	7.428%	$110.1782	$110.18	$110.20	$110.20
Purchase #7	$78.90	13.354%	$89.4363	$89.44	$89.45	$89.40
7 purchase totals =	$729.61		$781.9896	$781.99	$782.00	$782.10