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	$122.95	12.802%	$138.6901	$138.69	$138.70	$138.70
Purchase #2	$84.53	6.625%	$90.1301	$90.13	$90.15	$90.10
Purchase #3	$219.47	4.760%	$229.9168	$229.92	$229.90	$229.90
Purchase #4	$241.52	10.326%	$266.4594	$266.46	$266.45	$266.50
Purchase #5	$183.66	13.377%	$208.2282	$208.23	$208.25	$208.20
Purchase #6	$67.38	5.753%	$71.2564	$71.26	$71.25	$71.30
Purchase #7	$132.98	13.827%	$151.3671	$151.37	$151.35	$151.40
7 purchase totals =	$1,052.49		$1,156.0481	$1,156.06	$1,156.05	$1,156.10