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	$167.32	13.191%	$189.3912	$189.39	$189.40	$189.40
Purchase #2	$81.42	9.852%	$89.4415	$89.44	$89.45	$89.40
Purchase #3	$170.84	13.802%	$194.4193	$194.42	$194.40	$194.40
Purchase #4	$83.43	9.144%	$91.0588	$91.06	$91.05	$91.10
Purchase #5	$230.29	5.779%	$243.5985	$243.60	$243.60	$243.60
Purchase #6	$9.39	13.204%	$10.6299	$10.63	$10.65	$10.60
Purchase #7	$172.53	9.802%	$189.4414	$189.44	$189.45	$189.40
7 purchase totals =	$915.22		$1,007.9806	$1,007.98	$1,008.00	$1,007.90