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	$14.98	8.863%	$16.3077	$16.31	$16.30	$16.30
Purchase #2	$227.40	12.347%	$255.4771	$255.48	$255.50	$255.50
Purchase #3	$18.83	9.679%	$20.6526	$20.65	$20.65	$20.70
Purchase #4	$50.93	11.635%	$56.8557	$56.86	$56.85	$56.90
Purchase #5	$126.53	13.243%	$143.2864	$143.29	$143.30	$143.30
Purchase #6	$243.46	8.650%	$264.5193	$264.52	$264.50	$264.50
Purchase #7	$78.83	13.465%	$89.4445	$89.44	$89.45	$89.40
7 purchase totals =	$760.96		$846.5433	$846.55	$846.55	$846.60