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	$42.83	8.628%	$46.5254	$46.53	$46.55	$46.50
Purchase #2	$169.49	8.661%	$184.1695	$184.17	$184.15	$184.20
Purchase #3	$248.90	4.236%	$259.4434	$259.44	$259.45	$259.40
Purchase #4	$98.98	10.648%	$109.5194	$109.52	$109.50	$109.50
Purchase #5	$101.92	9.503%	$111.6055	$111.61	$111.60	$111.60
Purchase #6	$99.26	13.386%	$112.5469	$112.55	$112.55	$112.50
Purchase #7	$148.79	11.866%	$166.4454	$166.45	$166.45	$166.40
7 purchase totals =	$910.17		$990.2555	$990.27	$990.25	$990.10