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	$95.89	13.444%	$108.7815	$108.78	$108.80	$108.80
Purchase #2	$160.30	3.404%	$165.7566	$165.76	$165.75	$165.80
Purchase #3	$152.72	3.348%	$157.8331	$157.83	$157.85	$157.80
Purchase #4	$20.43	8.714%	$22.2103	$22.21	$22.20	$22.20
Purchase #5	$99.90	5.534%	$105.4285	$105.43	$105.45	$105.40
Purchase #6	$73.31	10.381%	$80.9203	$80.92	$80.90	$80.90
Purchase #7	$248.78	3.464%	$257.3977	$257.40	$257.40	$257.40
7 purchase totals =	$851.33		$898.3280	$898.33	$898.35	$898.30