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	$20.39	13.247%	$23.0911	$23.09	$23.10	$23.10
Purchase #2	$162.38	10.321%	$179.1392	$179.14	$179.15	$179.10
Purchase #3	$97.28	3.146%	$100.3404	$100.34	$100.35	$100.30
Purchase #4	$154.70	10.223%	$170.515	$170.52	$170.50	$170.50
Purchase #5	$42.94	5.445%	$45.2781	$45.28	$45.30	$45.30
Purchase #6	$61.90	5.172%	$65.1015	$65.10	$65.10	$65.10
Purchase #7	$250.32	4.485%	$261.5469	$261.55	$261.55	$261.50
7 purchase totals =	$789.91		$845.0122	$845.02	$845.05	$844.90