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	$247.68	12.598%	$278.8827	$278.88	$278.90	$278.90
Purchase #2	$132.94	3.356%	$137.4015	$137.40	$137.40	$137.40
Purchase #3	$179.48	10.513%	$198.3487	$198.35	$198.35	$198.30
Purchase #4	$131.74	9.454%	$144.1947	$144.19	$144.20	$144.20
Purchase #5	$58.75	4.286%	$61.268	$61.27	$61.25	$61.30
Purchase #6	$78.40	5.156%	$82.4423	$82.44	$82.45	$82.40
Purchase #7	$24.90	4.651%	$26.0581	$26.06	$26.05	$26.10
7 purchase totals =	$853.89		$928.5960	$928.59	$928.60	$928.60