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	$179.53	5.752%	$189.8566	$189.86	$189.85	$189.90
Purchase #2	$241.45	11.199%	$268.49	$268.49	$268.50	$268.50
Purchase #3	$179.68	6.559%	$191.4652	$191.47	$191.45	$191.50
Purchase #4	$98.47	7.227%	$105.5864	$105.59	$105.60	$105.60
Purchase #5	$116.39	9.613%	$127.5786	$127.58	$127.60	$127.60
Purchase #6	$46.65	3.401%	$48.2366	$48.24	$48.25	$48.20
Purchase #7	$147.99	3.569%	$153.2718	$153.27	$153.25	$153.30
7 purchase totals =	$1,010.16		$1,084.4852	$1,084.50	$1,084.50	$1,084.60