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	$159.92	10.114%	$176.0943	$176.09	$176.10	$176.10
Purchase #2	$180.57	12.597%	$203.3164	$203.32	$203.30	$203.30
Purchase #3	$162.88	12.872%	$183.8459	$183.85	$183.85	$183.80
Purchase #4	$38.74	3.557%	$40.118	$40.12	$40.10	$40.10
Purchase #5	$105.78	5.247%	$111.3303	$111.33	$111.35	$111.30
Purchase #6	$172.91	4.567%	$180.8068	$180.81	$180.80	$180.80
Purchase #7	$207.81	4.480%	$217.1199	$217.12	$217.10	$217.10
7 purchase totals =	$1,028.61		$1,112.6316	$1,112.64	$1,112.60	$1,112.50