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	$26.77	8.747%	$29.1116	$29.11	$29.10	$29.10
Purchase #2	$139.94	3.221%	$144.4475	$144.45	$144.45	$144.40
Purchase #3	$83.72	3.440%	$86.6	$86.60	$86.60	$86.60
Purchase #4	$166.60	4.328%	$173.8104	$173.81	$173.80	$173.80
Purchase #5	$183.86	8.728%	$199.9073	$199.91	$199.90	$199.90
Purchase #6	$49.32	8.674%	$53.598	$53.60	$53.60	$53.60
Purchase #7	$218.60	12.458%	$245.8332	$245.83	$245.85	$245.80
7 purchase totals =	$868.81		$933.3080	$933.31	$933.30	$933.20