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	$159.60	6.868%	$170.5613	$170.56	$170.55	$170.60
Purchase #2	$125.72	4.110%	$130.8871	$130.89	$130.90	$130.90
Purchase #3	$245.27	6.480%	$261.1635	$261.16	$261.15	$261.20
Purchase #4	$134.56	12.206%	$150.9844	$150.98	$151.00	$151.00
Purchase #5	$119.60	7.161%	$128.1646	$128.16	$128.15	$128.20
Purchase #6	$111.31	13.790%	$126.6596	$126.66	$126.65	$126.70
Purchase #7	$228.63	13.240%	$258.9006	$258.90	$258.90	$258.90
7 purchase totals =	$1,124.69		$1,227.3211	$1,227.31	$1,227.30	$1,227.50