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	$223.85	4.689%	$234.3463	$234.35	$234.35	$234.30
Purchase #2	$116.92	8.738%	$127.1365	$127.14	$127.15	$127.10
Purchase #3	$89.43	12.357%	$100.4809	$100.48	$100.50	$100.50
Purchase #4	$183.55	10.794%	$203.3624	$203.36	$203.35	$203.40
Purchase #5	$159.94	11.576%	$178.4547	$178.45	$178.45	$178.50
Purchase #6	$183.86	12.371%	$206.6053	$206.61	$206.60	$206.60
Purchase #7	$114.97	12.680%	$129.5482	$129.55	$129.55	$129.50
7 purchase totals =	$1,072.52		$1,179.9343	$1,179.94	$1,179.95	$1,179.90