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	$32.85	4.576%	$34.3532	$34.35	$34.35	$34.40
Purchase #2	$183.94	6.867%	$196.5712	$196.57	$196.55	$196.60
Purchase #3	$128.54	7.270%	$137.8849	$137.88	$137.90	$137.90
Purchase #4	$66.62	9.335%	$72.839	$72.84	$72.85	$72.80
Purchase #5	$106.56	4.336%	$111.1804	$111.18	$111.20	$111.20
Purchase #6	$137.30	12.435%	$154.3733	$154.37	$154.35	$154.40
Purchase #7	$22.26	10.373%	$24.569	$24.57	$24.55	$24.60
7 purchase totals =	$678.07		$731.7710	$731.76	$731.75	$731.90