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	$27.58	7.362%	$29.6104	$29.61	$29.60	$29.60
Purchase #2	$134.99	7.446%	$145.0414	$145.04	$145.05	$145.00
Purchase #3	$105.77	5.736%	$111.837	$111.84	$111.85	$111.80
Purchase #4	$188.32	9.199%	$205.6436	$205.64	$205.65	$205.60
Purchase #5	$125.52	9.160%	$137.0176	$137.02	$137.00	$137.00
Purchase #6	$242.36	5.547%	$255.8037	$255.80	$255.80	$255.80
Purchase #7	$86.82	3.605%	$89.9499	$89.95	$89.95	$89.90
7 purchase totals =	$911.36		$974.9036	$974.90	$974.90	$974.70