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	$14.86	10.641%	$16.4413	$16.44	$16.45	$16.40
Purchase #2	$65.33	9.337%	$71.4299	$71.43	$71.45	$71.40
Purchase #3	$172.80	13.501%	$196.1297	$196.13	$196.15	$196.10
Purchase #4	$223.68	4.247%	$233.1797	$233.18	$233.20	$233.20
Purchase #5	$231.81	3.836%	$240.7022	$240.70	$240.70	$240.70
Purchase #6	$115.79	6.295%	$123.079	$123.08	$123.10	$123.10
Purchase #7	$89.25	9.130%	$97.3985	$97.40	$97.40	$97.40
7 purchase totals =	$913.52		$978.3603	$978.36	$978.45	$978.30