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	$39.31	4.445%	$41.0573	$41.06	$41.05	$41.10
Purchase #2	$236.28	8.107%	$255.4352	$255.44	$255.45	$255.40
Purchase #3	$31.49	9.476%	$34.474	$34.47	$34.45	$34.50
Purchase #4	$38.50	3.102%	$39.6943	$39.69	$39.70	$39.70
Purchase #5	$194.94	10.752%	$215.8999	$215.90	$215.90	$215.90
Purchase #6	$187.60	13.237%	$212.4326	$212.43	$212.45	$212.40
Purchase #7	$41.67	9.323%	$45.5549	$45.55	$45.55	$45.60
7 purchase totals =	$769.79		$844.5482	$844.54	$844.55	$844.60