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	$146.28	8.753%	$159.0839	$159.08	$159.10	$159.10
Purchase #2	$102.27	4.547%	$106.9202	$106.92	$106.90	$106.90
Purchase #3	$227.42	6.110%	$241.3154	$241.32	$241.30	$241.30
Purchase #4	$143.39	6.333%	$152.4709	$152.47	$152.45	$152.50
Purchase #5	$44.51	9.612%	$48.7883	$48.79	$48.80	$48.80
Purchase #6	$79.96	12.212%	$89.7247	$89.72	$89.70	$89.70
Purchase #7	$57.63	8.109%	$62.3032	$62.30	$62.30	$62.30
7 purchase totals =	$801.46		$860.6066	$860.60	$860.55	$860.60