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	$11.45	6.518%	$12.1963	$12.20	$12.20	$12.20
Purchase #2	$66.25	9.868%	$72.7876	$72.79	$72.80	$72.80
Purchase #3	$229.65	4.829%	$240.7398	$240.74	$240.75	$240.70
Purchase #4	$30.67	3.792%	$31.833	$31.83	$31.85	$31.80
Purchase #5	$172.91	6.776%	$184.6264	$184.63	$184.65	$184.60
Purchase #6	$43.39	3.804%	$45.0406	$45.04	$45.05	$45.00
Purchase #7	$123.80	5.717%	$130.8776	$130.88	$130.90	$130.90
7 purchase totals =	$678.12		$718.1013	$718.11	$718.20	$718.00