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	$131.56	12.827%	$148.4352	$148.44	$148.45	$148.40
Purchase #2	$103.91	11.696%	$116.0633	$116.06	$116.05	$116.10
Purchase #3	$67.57	7.822%	$72.8553	$72.86	$72.85	$72.90
Purchase #4	$140.96	5.370%	$148.5296	$148.53	$148.55	$148.50
Purchase #5	$115.32	7.716%	$124.2181	$124.22	$124.20	$124.20
Purchase #6	$20.86	11.624%	$23.2848	$23.28	$23.30	$23.30
Purchase #7	$33.43	11.235%	$37.1859	$37.19	$37.20	$37.20
7 purchase totals =	$613.61		$670.5722	$670.58	$670.60	$670.60