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	$243.65	13.115%	$275.6047	$275.60	$275.60	$275.60
Purchase #2	$133.31	10.396%	$147.1689	$147.17	$147.15	$147.20
Purchase #3	$131.70	9.730%	$144.5144	$144.51	$144.50	$144.50
Purchase #4	$51.91	4.628%	$54.3124	$54.31	$54.30	$54.30
Purchase #5	$169.65	12.254%	$190.4389	$190.44	$190.45	$190.40
Purchase #6	$220.98	8.110%	$238.9015	$238.90	$238.90	$238.90
Purchase #7	$192.63	9.624%	$211.1687	$211.17	$211.15	$211.20
7 purchase totals =	$1,143.83		$1,262.1095	$1,262.10	$1,262.05	$1,262.10