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	$168.55	5.372%	$177.6045	$177.60	$177.60	$177.60
Purchase #2	$144.48	10.817%	$160.1084	$160.11	$160.10	$160.10
Purchase #3	$34.88	12.579%	$39.2676	$39.27	$39.25	$39.30
Purchase #4	$128.76	3.198%	$132.8777	$132.88	$132.90	$132.90
Purchase #5	$134.33	8.741%	$146.0718	$146.07	$146.05	$146.10
Purchase #6	$52.46	13.654%	$59.6229	$59.62	$59.60	$59.60
Purchase #7	$116.29	5.862%	$123.1069	$123.11	$123.10	$123.10
7 purchase totals =	$779.75		$838.6598	$838.66	$838.60	$838.70