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	$29.33	12.385%	$32.9625	$32.96	$32.95	$33.00
Purchase #2	$122.45	7.262%	$131.3423	$131.34	$131.35	$131.30
Purchase #3	$56.87	5.428%	$59.9569	$59.96	$59.95	$60.00
Purchase #4	$18.25	12.140%	$20.4656	$20.47	$20.45	$20.50
Purchase #5	$129.63	3.330%	$133.9467	$133.95	$133.95	$133.90
Purchase #6	$107.90	8.125%	$116.6669	$116.67	$116.65	$116.70
Purchase #7	$84.51	6.819%	$90.2727	$90.27	$90.25	$90.30
7 purchase totals =	$548.94		$585.6136	$585.62	$585.55	$585.70