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	$40.43	5.820%	$42.783	$42.78	$42.80	$42.80
Purchase #2	$144.64	9.437%	$158.2897	$158.29	$158.30	$158.30
Purchase #3	$67.65	7.263%	$72.5634	$72.56	$72.55	$72.60
Purchase #4	$216.92	6.188%	$230.343	$230.34	$230.35	$230.30
Purchase #5	$115.62	12.803%	$130.4228	$130.42	$130.40	$130.40
Purchase #6	$34.55	11.314%	$38.459	$38.46	$38.45	$38.50
Purchase #7	$41.95	8.160%	$45.3731	$45.37	$45.35	$45.40
7 purchase totals =	$661.76		$718.2340	$718.22	$718.20	$718.30