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	$83.91	6.553%	$89.4086	$89.41	$89.40	$89.40
Purchase #2	$219.92	7.434%	$236.2689	$236.27	$236.25	$236.30
Purchase #3	$123.31	5.802%	$130.4644	$130.46	$130.45	$130.50
Purchase #4	$56.76	11.254%	$63.1478	$63.15	$63.15	$63.10
Purchase #5	$126.41	8.827%	$137.5682	$137.57	$137.55	$137.60
Purchase #6	$75.74	12.596%	$85.2802	$85.28	$85.30	$85.30
Purchase #7	$153.45	12.453%	$172.5591	$172.56	$172.55	$172.60
7 purchase totals =	$839.50		$914.6972	$914.70	$914.65	$914.80