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	$127.69	6.716%	$136.2657	$136.27	$136.25	$136.30
Purchase #2	$97.74	6.618%	$104.2084	$104.21	$104.20	$104.20
Purchase #3	$144.78	10.207%	$159.5577	$159.56	$159.55	$159.60
Purchase #4	$249.65	12.382%	$280.5617	$280.56	$280.55	$280.60
Purchase #5	$9.50	13.553%	$10.7875	$10.79	$10.80	$10.80
Purchase #6	$169.52	10.414%	$187.1738	$187.17	$187.15	$187.20
Purchase #7	$126.49	11.754%	$141.3576	$141.36	$141.35	$141.40
7 purchase totals =	$925.37		$1,019.9124	$1,019.92	$1,019.85	$1,020.10