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	$86.41	4.493%	$90.2924	$90.29	$90.30	$90.30
Purchase #2	$236.76	10.697%	$262.0862	$262.09	$262.10	$262.10
Purchase #3	$82.48	6.768%	$88.0622	$88.06	$88.05	$88.10
Purchase #4	$70.48	11.557%	$78.6254	$78.63	$78.65	$78.60
Purchase #5	$25.43	10.560%	$28.1154	$28.12	$28.10	$28.10
Purchase #6	$102.49	5.290%	$107.9117	$107.91	$107.90	$107.90
Purchase #7	$132.86	13.305%	$150.537	$150.54	$150.55	$150.50
7 purchase totals =	$736.91		$805.6303	$805.64	$805.65	$805.60