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	$130.35	10.473%	$144.0016	$144.00	$144.00	$144.00
Purchase #2	$71.95	11.251%	$80.0451	$80.05	$80.05	$80.00
Purchase #3	$14.58	5.558%	$15.3904	$15.39	$15.40	$15.40
Purchase #4	$96.77	9.109%	$105.5848	$105.58	$105.60	$105.60
Purchase #5	$128.85	12.170%	$144.531	$144.53	$144.55	$144.50
Purchase #6	$102.47	6.473%	$109.1029	$109.10	$109.10	$109.10
Purchase #7	$153.26	3.720%	$158.9613	$158.96	$158.95	$159.00
7 purchase totals =	$698.23		$757.6171	$757.61	$757.65	$757.60