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	$56.98	8.640%	$61.9031	$61.90	$61.90	$61.90
Purchase #2	$34.53	12.727%	$38.9246	$38.92	$38.90	$38.90
Purchase #3	$132.41	3.793%	$137.4323	$137.43	$137.45	$137.40
Purchase #4	$28.59	7.450%	$30.72	$30.72	$30.70	$30.70
Purchase #5	$249.47	10.709%	$276.1857	$276.19	$276.20	$276.20
Purchase #6	$50.30	9.641%	$55.1494	$55.15	$55.15	$55.10
Purchase #7	$91.65	9.174%	$100.058	$100.06	$100.05	$100.10
7 purchase totals =	$643.93		$700.3731	$700.37	$700.35	$700.30