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	$143.97	3.368%	$148.8189	$148.82	$148.80	$148.80
Purchase #2	$165.44	12.233%	$185.6783	$185.68	$185.70	$185.70
Purchase #3	$77.32	10.443%	$85.3945	$85.39	$85.40	$85.40
Purchase #4	$22.47	13.559%	$25.5167	$25.52	$25.50	$25.50
Purchase #5	$53.79	10.828%	$59.6144	$59.61	$59.60	$59.60
Purchase #6	$222.94	5.860%	$236.0043	$236.00	$236.00	$236.00
Purchase #7	$34.78	11.145%	$38.6562	$38.66	$38.65	$38.70
7 purchase totals =	$720.71		$779.6833	$779.68	$779.65	$779.70