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	$31.70	4.521%	$33.1332	$33.13	$33.15	$33.10
Purchase #2	$99.77	10.244%	$109.9904	$109.99	$110.00	$110.00
Purchase #3	$97.45	8.640%	$105.8697	$105.87	$105.85	$105.90
Purchase #4	$235.95	11.839%	$263.8841	$263.88	$263.90	$263.90
Purchase #5	$20.80	3.480%	$21.5238	$21.52	$21.50	$21.50
Purchase #6	$136.57	13.803%	$155.4208	$155.42	$155.40	$155.40
Purchase #7	$187.83	4.417%	$196.1265	$196.13	$196.15	$196.10
7 purchase totals =	$810.07		$885.9485	$885.94	$885.95	$885.90