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	5.233%	$137.1712	$137.17	$137.15	$137.20
Purchase #2	$83.62	7.176%	$89.6206	$89.62	$89.60	$89.60
Purchase #3	$25.81	5.773%	$27.3	$27.30	$27.30	$27.30
Purchase #4	$115.71	10.152%	$127.4569	$127.46	$127.45	$127.50
Purchase #5	$59.44	5.256%	$62.5642	$62.56	$62.55	$62.60
Purchase #6	$47.54	8.653%	$51.6536	$51.65	$51.65	$51.70
Purchase #7	$88.35	8.672%	$96.0117	$96.01	$96.00	$96.00
7 purchase totals =	$550.82		$591.7782	$591.77	$591.70	$591.90