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	$19.43	3.276%	$20.0665	$20.07	$20.05	$20.10
Purchase #2	$108.77	13.416%	$123.3626	$123.36	$123.35	$123.40
Purchase #3	$138.70	11.766%	$155.0194	$155.02	$155.00	$155.00
Purchase #4	$153.64	9.250%	$167.8517	$167.85	$167.85	$167.90
Purchase #5	$104.46	7.794%	$112.6016	$112.60	$112.60	$112.60
Purchase #6	$142.31	11.634%	$158.8663	$158.87	$158.85	$158.90
Purchase #7	$85.52	6.846%	$91.3747	$91.37	$91.35	$91.40
7 purchase totals =	$752.83		$829.1428	$829.14	$829.05	$829.30