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	$7.35	3.583%	$7.6134	$7.61	$7.60	$7.60
Purchase #2	$48.75	7.638%	$52.4735	$52.47	$52.45	$52.50
Purchase #3	$146.55	3.216%	$151.263	$151.26	$151.25	$151.30
Purchase #4	$46.62	9.504%	$51.0508	$51.05	$51.05	$51.10
Purchase #5	$67.36	6.417%	$71.6825	$71.68	$71.70	$71.70
Purchase #6	$155.75	7.475%	$167.3923	$167.39	$167.40	$167.40
Purchase #7	$80.46	12.834%	$90.7862	$90.79	$90.80	$90.80
7 purchase totals =	$552.84		$592.2617	$592.25	$592.25	$592.40