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	$230.60	4.242%	$240.3821	$240.38	$240.40	$240.40
Purchase #2	$23.93	5.498%	$25.2457	$25.25	$25.25	$25.20
Purchase #3	$100.31	10.400%	$110.7422	$110.74	$110.75	$110.70
Purchase #4	$32.78	10.134%	$36.1019	$36.10	$36.10	$36.10
Purchase #5	$67.89	5.314%	$71.4977	$71.50	$71.50	$71.50
Purchase #6	$43.28	12.238%	$48.5766	$48.58	$48.60	$48.60
Purchase #7	$46.33	9.118%	$50.5544	$50.55	$50.55	$50.60
7 purchase totals =	$545.12		$583.1006	$583.10	$583.15	$583.10