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	$80.72	10.597%	$89.2739	$89.27	$89.25	$89.30
Purchase #2	$175.84	13.563%	$199.6892	$199.69	$199.70	$199.70
Purchase #3	$148.97	12.490%	$167.5764	$167.58	$167.60	$167.60
Purchase #4	$78.40	9.112%	$85.5438	$85.54	$85.55	$85.50
Purchase #5	$46.65	9.436%	$51.0519	$51.05	$51.05	$51.10
Purchase #6	$108.80	3.176%	$112.2555	$112.26	$112.25	$112.30
Purchase #7	$123.41	5.728%	$130.4789	$130.48	$130.50	$130.50
7 purchase totals =	$762.79		$835.8696	$835.87	$835.90	$836.00