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	$134.52	7.509%	$144.6211	$144.62	$144.60	$144.60
Purchase #2	$175.79	5.287%	$185.084	$185.08	$185.10	$185.10
Purchase #3	$225.56	4.469%	$235.6403	$235.64	$235.65	$235.60
Purchase #4	$153.48	8.429%	$166.4168	$166.42	$166.40	$166.40
Purchase #5	$106.89	11.623%	$119.3138	$119.31	$119.30	$119.30
Purchase #6	$76.99	7.640%	$82.872	$82.87	$82.85	$82.90
Purchase #7	$6.68	11.872%	$7.473	$7.47	$7.45	$7.50
7 purchase totals =	$879.91		$941.4210	$941.41	$941.35	$941.40