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	$138.38	4.337%	$144.3815	$144.38	$144.40	$144.40
Purchase #2	$210.83	7.332%	$226.2881	$226.29	$226.30	$226.30
Purchase #3	$182.63	3.142%	$188.3682	$188.37	$188.35	$188.40
Purchase #4	$201.76	10.385%	$222.7128	$222.71	$222.70	$222.70
Purchase #5	$216.73	9.308%	$236.9032	$236.90	$236.90	$236.90
Purchase #6	$116.85	13.424%	$132.5359	$132.54	$132.55	$132.50
Purchase #7	$175.52	12.158%	$196.8597	$196.86	$196.85	$196.90
7 purchase totals =	$1,242.70		$1,348.0494	$1,348.05	$1,348.05	$1,348.10