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	$233.81	6.843%	$249.8096	$249.81	$249.80	$249.80
Purchase #2	$151.54	5.329%	$159.6156	$159.62	$159.60	$159.60
Purchase #3	$147.64	8.222%	$159.779	$159.78	$159.80	$159.80
Purchase #4	$45.40	13.606%	$51.5771	$51.58	$51.60	$51.60
Purchase #5	$39.66	10.123%	$43.6748	$43.67	$43.65	$43.70
Purchase #6	$141.95	8.833%	$154.4884	$154.49	$154.50	$154.50
Purchase #7	$140.32	10.730%	$155.3763	$155.38	$155.40	$155.40
7 purchase totals =	$900.32		$974.3208	$974.33	$974.35	$974.40