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	$35.63	6.552%	$37.9645	$37.96	$37.95	$38.00
Purchase #2	$95.82	4.384%	$100.0207	$100.02	$100.00	$100.00
Purchase #3	$62.69	6.753%	$66.9235	$66.92	$66.90	$66.90
Purchase #4	$68.73	5.723%	$72.6634	$72.66	$72.65	$72.70
Purchase #5	$225.72	13.377%	$255.9146	$255.91	$255.90	$255.90
Purchase #6	$211.85	6.286%	$225.1669	$225.17	$225.15	$225.20
Purchase #7	$138.37	12.848%	$156.1478	$156.15	$156.15	$156.10
7 purchase totals =	$838.81		$914.8014	$914.79	$914.70	$914.80