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	$156.83	5.789%	$165.9089	$165.91	$165.90	$165.90
Purchase #2	$104.83	6.427%	$111.5674	$111.57	$111.55	$111.60
Purchase #3	$220.68	6.209%	$234.382	$234.38	$234.40	$234.40
Purchase #4	$35.38	6.191%	$37.5704	$37.57	$37.55	$37.60
Purchase #5	$139.46	12.769%	$157.2676	$157.27	$157.25	$157.30
Purchase #6	$96.79	7.601%	$104.147	$104.15	$104.15	$104.10
Purchase #7	$116.75	9.523%	$127.8681	$127.87	$127.85	$127.90
7 purchase totals =	$870.72		$938.7114	$938.72	$938.65	$938.80