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	$48.27	5.679%	$51.0113	$51.01	$51.00	$51.00
Purchase #2	$187.92	4.657%	$196.6714	$196.67	$196.65	$196.70
Purchase #3	$116.94	13.310%	$132.5047	$132.50	$132.50	$132.50
Purchase #4	$218.64	11.625%	$244.0569	$244.06	$244.05	$244.10
Purchase #5	$54.78	8.322%	$59.3388	$59.34	$59.35	$59.30
Purchase #6	$58.31	12.542%	$65.6232	$65.62	$65.60	$65.60
Purchase #7	$61.27	5.597%	$64.6993	$64.70	$64.70	$64.70
7 purchase totals =	$746.13		$813.9056	$813.90	$813.85	$813.90