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	$51.61	13.455%	$58.5541	$58.55	$58.55	$58.60
Purchase #2	$26.38	8.111%	$28.5197	$28.52	$28.50	$28.50
Purchase #3	$57.79	10.485%	$63.8493	$63.85	$63.85	$63.80
Purchase #4	$96.83	8.804%	$105.3549	$105.35	$105.35	$105.40
Purchase #5	$227.87	11.431%	$253.9178	$253.92	$253.90	$253.90
Purchase #6	$80.85	6.179%	$85.8457	$85.85	$85.85	$85.80
Purchase #7	$68.72	13.594%	$78.0618	$78.06	$78.05	$78.10
7 purchase totals =	$610.05		$674.1033	$674.10	$674.05	$674.10