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	$11.75	9.753%	$12.896	$12.90	$12.90	$12.90
Purchase #2	$143.58	8.766%	$156.1662	$156.17	$156.15	$156.20
Purchase #3	$173.76	11.334%	$193.454	$193.45	$193.45	$193.50
Purchase #4	$187.60	12.713%	$211.4496	$211.45	$211.45	$211.40
Purchase #5	$135.40	13.179%	$153.2444	$153.24	$153.25	$153.20
Purchase #6	$139.86	6.808%	$149.3817	$149.38	$149.40	$149.40
Purchase #7	$164.67	12.421%	$185.1237	$185.12	$185.10	$185.10
7 purchase totals =	$956.62		$1,061.7156	$1,061.71	$1,061.70	$1,061.70