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	$27.68	7.546%	$29.7687	$29.77	$29.75	$29.80
Purchase #2	$35.46	11.366%	$39.4904	$39.49	$39.50	$39.50
Purchase #3	$50.52	7.196%	$54.1554	$54.16	$54.15	$54.20
Purchase #4	$59.62	9.233%	$65.1247	$65.12	$65.10	$65.10
Purchase #5	$53.63	10.809%	$59.4269	$59.43	$59.45	$59.40
Purchase #6	$128.45	5.415%	$135.4056	$135.41	$135.40	$135.40
Purchase #7	$46.87	3.357%	$48.4434	$48.44	$48.45	$48.40
7 purchase totals =	$402.23		$431.8151	$431.82	$431.80	$431.80