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	$183.52	10.640%	$203.0465	$203.05	$203.05	$203.00
Purchase #2	$53.41	4.135%	$55.6185	$55.62	$55.60	$55.60
Purchase #3	$45.82	9.403%	$50.1285	$50.13	$50.15	$50.10
Purchase #4	$214.33	11.428%	$238.8236	$238.82	$238.80	$238.80
Purchase #5	$211.69	5.114%	$222.5158	$222.52	$222.50	$222.50
Purchase #6	$93.71	10.243%	$103.3087	$103.31	$103.30	$103.30
Purchase #7	$41.65	8.327%	$45.1182	$45.12	$45.10	$45.10
7 purchase totals =	$844.13		$918.5598	$918.57	$918.50	$918.40