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	$57.47	10.248%	$63.3595	$63.36	$63.35	$63.40
Purchase #2	$99.82	4.573%	$104.3848	$104.38	$104.40	$104.40
Purchase #3	$130.36	8.434%	$141.3546	$141.35	$141.35	$141.40
Purchase #4	$99.92	10.643%	$110.5545	$110.55	$110.55	$110.60
Purchase #5	$139.45	9.205%	$152.2864	$152.29	$152.30	$152.30
Purchase #6	$88.90	12.582%	$100.0854	$100.09	$100.10	$100.10
Purchase #7	$172.26	7.139%	$184.5576	$184.56	$184.55	$184.60
7 purchase totals =	$788.18		$856.5828	$856.58	$856.60	$856.80