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	$115.35	4.231%	$120.2305	$120.23	$120.25	$120.20
Purchase #2	$175.56	7.802%	$189.2572	$189.26	$189.25	$189.30
Purchase #3	$57.27	3.666%	$59.3695	$59.37	$59.35	$59.40
Purchase #4	$16.96	3.852%	$17.6133	$17.61	$17.60	$17.60
Purchase #5	$222.32	8.744%	$241.7597	$241.76	$241.75	$241.80
Purchase #6	$177.26	8.110%	$191.6358	$191.64	$191.65	$191.60
Purchase #7	$115.65	10.258%	$127.5134	$127.51	$127.50	$127.50
7 purchase totals =	$880.37		$947.3794	$947.38	$947.35	$947.40