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	$170.83	4.428%	$178.3944	$178.39	$178.40	$178.40
Purchase #2	$130.50	10.777%	$144.564	$144.56	$144.55	$144.60
Purchase #3	$9.37	12.585%	$10.5492	$10.55	$10.55	$10.50
Purchase #4	$196.62	3.624%	$203.7455	$203.75	$203.75	$203.70
Purchase #5	$218.47	12.268%	$245.2719	$245.27	$245.25	$245.30
Purchase #6	$118.52	13.178%	$134.1386	$134.14	$134.15	$134.10
Purchase #7	$78.60	9.480%	$86.0513	$86.05	$86.05	$86.10
7 purchase totals =	$922.91		$1,002.7149	$1,002.71	$1,002.70	$1,002.70