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	$116.91	11.677%	$130.5616	$130.56	$130.55	$130.60
Purchase #2	$163.49	12.457%	$183.8559	$183.86	$183.85	$183.90
Purchase #3	$175.64	7.441%	$188.7094	$188.71	$188.70	$188.70
Purchase #4	$85.72	11.325%	$95.4278	$95.43	$95.45	$95.40
Purchase #5	$151.91	3.297%	$156.9185	$156.92	$156.90	$156.90
Purchase #6	$225.56	13.375%	$255.7287	$255.73	$255.75	$255.70
Purchase #7	$75.98	3.420%	$78.5785	$78.58	$78.60	$78.60
7 purchase totals =	$995.21		$1,089.7804	$1,089.79	$1,089.80	$1,089.80