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	$167.76	12.410%	$188.579	$188.58	$188.60	$188.60
Purchase #2	$137.52	6.327%	$146.2209	$146.22	$146.20	$146.20
Purchase #3	$13.43	4.505%	$14.035	$14.04	$14.05	$14.00
Purchase #4	$17.96	10.534%	$19.8519	$19.85	$19.85	$19.90
Purchase #5	$219.65	8.558%	$238.4476	$238.45	$238.45	$238.40
Purchase #6	$167.42	10.627%	$185.2117	$185.21	$185.20	$185.20
Purchase #7	$151.69	12.438%	$170.5572	$170.56	$170.55	$170.60
7 purchase totals =	$875.43		$962.9033	$962.91	$962.90	$962.90