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	$41.49	3.393%	$42.8978	$42.90	$42.90	$42.90
Purchase #2	$246.51	8.162%	$266.6301	$266.63	$266.65	$266.60
Purchase #3	$120.72	13.580%	$137.1138	$137.11	$137.10	$137.10
Purchase #4	$41.99	7.793%	$45.2623	$45.26	$45.25	$45.30
Purchase #5	$90.55	9.162%	$98.8462	$98.85	$98.85	$98.80
Purchase #6	$122.64	13.555%	$139.2639	$139.26	$139.25	$139.30
Purchase #7	$105.64	5.146%	$111.0762	$111.08	$111.10	$111.10
7 purchase totals =	$769.54		$841.0903	$841.09	$841.10	$841.10