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	$7.25	3.388%	$7.4956	$7.50	$7.50	$7.50
Purchase #2	$171.54	4.230%	$178.7961	$178.80	$178.80	$178.80
Purchase #3	$119.29	3.136%	$123.0309	$123.03	$123.05	$123.00
Purchase #4	$41.27	4.471%	$43.1152	$43.12	$43.10	$43.10
Purchase #5	$10.25	11.706%	$11.4499	$11.45	$11.45	$11.40
Purchase #6	$21.80	13.817%	$24.8121	$24.81	$24.80	$24.80
Purchase #7	$74.42	7.511%	$80.0097	$80.01	$80.00	$80.00
7 purchase totals =	$445.82		$468.7095	$468.72	$468.70	$468.60