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	$37.39	5.584%	$39.4779	$39.48	$39.50	$39.50
Purchase #2	$159.67	9.782%	$175.2889	$175.29	$175.30	$175.30
Purchase #3	$57.81	10.822%	$64.0662	$64.07	$64.05	$64.10
Purchase #4	$127.46	4.602%	$133.3257	$133.33	$133.35	$133.30
Purchase #5	$151.48	5.871%	$160.3734	$160.37	$160.35	$160.40
Purchase #6	$123.74	3.380%	$127.9224	$127.92	$127.90	$127.90
Purchase #7	$59.84	10.548%	$66.1519	$66.15	$66.15	$66.20
7 purchase totals =	$717.39		$766.6064	$766.61	$766.60	$766.70