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	$35.67	7.820%	$38.4594	$38.46	$38.45	$38.50
Purchase #2	$149.56	6.565%	$159.3786	$159.38	$159.40	$159.40
Purchase #3	$102.99	5.331%	$108.4804	$108.48	$108.50	$108.50
Purchase #4	$107.87	3.744%	$111.9087	$111.91	$111.90	$111.90
Purchase #5	$19.47	3.396%	$20.1312	$20.13	$20.15	$20.10
Purchase #6	$55.40	10.651%	$61.3007	$61.30	$61.30	$61.30
Purchase #7	$134.70	13.709%	$153.166	$153.17	$153.15	$153.20
7 purchase totals =	$605.66		$652.8250	$652.83	$652.85	$652.90