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	$177.69	4.571%	$185.8122	$185.81	$185.80	$185.80
Purchase #2	$169.69	6.476%	$180.6791	$180.68	$180.70	$180.70
Purchase #3	$35.75	10.593%	$39.537	$39.54	$39.55	$39.50
Purchase #4	$98.56	13.286%	$111.6547	$111.65	$111.65	$111.70
Purchase #5	$30.60	9.294%	$33.444	$33.44	$33.45	$33.40
Purchase #6	$237.66	4.595%	$248.5805	$248.58	$248.60	$248.60
Purchase #7	$180.71	10.693%	$200.0333	$200.03	$200.05	$200.00
7 purchase totals =	$930.66		$999.7408	$999.73	$999.80	$999.70