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	$123.70	8.622%	$134.3654	$134.37	$134.35	$134.40
Purchase #2	$145.40	13.757%	$165.4027	$165.40	$165.40	$165.40
Purchase #3	$50.59	3.125%	$52.1709	$52.17	$52.15	$52.20
Purchase #4	$73.59	12.223%	$82.5849	$82.58	$82.60	$82.60
Purchase #5	$19.76	9.580%	$21.653	$21.65	$21.65	$21.70
Purchase #6	$220.32	6.102%	$233.7639	$233.76	$233.75	$233.80
Purchase #7	$141.62	10.654%	$156.7082	$156.71	$156.70	$156.70
7 purchase totals =	$774.98		$846.6490	$846.64	$846.60	$846.80