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	$154.36	12.258%	$173.2814	$173.28	$173.30	$173.30
Purchase #2	$241.89	13.700%	$275.0289	$275.03	$275.05	$275.00
Purchase #3	$101.66	3.792%	$105.5149	$105.51	$105.50	$105.50
Purchase #4	$146.45	9.477%	$160.3291	$160.33	$160.35	$160.30
Purchase #5	$119.89	5.867%	$126.9239	$126.92	$126.90	$126.90
Purchase #6	$155.25	3.293%	$160.3624	$160.36	$160.35	$160.40
Purchase #7	$125.59	5.808%	$132.8843	$132.88	$132.90	$132.90
7 purchase totals =	$1,045.09		$1,134.3249	$1,134.31	$1,134.35	$1,134.30