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	$26.63	11.806%	$29.7739	$29.77	$29.75	$29.80
Purchase #2	$107.56	3.259%	$111.0654	$111.07	$111.05	$111.10
Purchase #3	$94.37	8.268%	$102.1725	$102.17	$102.15	$102.20
Purchase #4	$152.30	10.345%	$168.0554	$168.06	$168.05	$168.10
Purchase #5	$95.83	4.248%	$99.9009	$99.90	$99.90	$99.90
Purchase #6	$230.40	12.787%	$259.8612	$259.86	$259.85	$259.90
Purchase #7	$117.78	5.869%	$124.6925	$124.69	$124.70	$124.70
7 purchase totals =	$824.87		$895.5218	$895.52	$895.45	$895.70