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	$24.79	11.157%	$27.5558	$27.56	$27.55	$27.60
Purchase #2	$40.27	6.710%	$42.9721	$42.97	$42.95	$43.00
Purchase #3	$111.90	13.729%	$127.2628	$127.26	$127.25	$127.30
Purchase #4	$157.97	4.856%	$165.641	$165.64	$165.65	$165.60
Purchase #5	$132.36	12.582%	$149.0135	$149.01	$149.00	$149.00
Purchase #6	$129.81	11.550%	$144.8031	$144.80	$144.80	$144.80
Purchase #7	$91.39	8.721%	$99.3601	$99.36	$99.35	$99.40
7 purchase totals =	$688.49		$756.6084	$756.60	$756.55	$756.70