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	$10.91	9.773%	$11.9762	$11.98	$12.00	$12.00
Purchase #2	$73.60	6.143%	$78.1212	$78.12	$78.10	$78.10
Purchase #3	$141.98	4.609%	$148.5239	$148.52	$148.50	$148.50
Purchase #4	$54.44	13.258%	$61.6577	$61.66	$61.65	$61.70
Purchase #5	$88.41	11.543%	$98.6152	$98.62	$98.60	$98.60
Purchase #6	$78.91	9.565%	$86.4577	$86.46	$86.45	$86.50
Purchase #7	$103.75	12.233%	$116.4417	$116.44	$116.45	$116.40
7 purchase totals =	$552.00		$601.7936	$601.80	$601.75	$601.80