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	$150.48	5.776%	$159.1717	$159.17	$159.15	$159.20
Purchase #2	$140.30	10.437%	$154.9431	$154.94	$154.95	$154.90
Purchase #3	$169.82	5.137%	$178.5437	$178.54	$178.55	$178.50
Purchase #4	$54.55	12.692%	$61.4735	$61.47	$61.45	$61.50
Purchase #5	$143.61	11.536%	$160.1768	$160.18	$160.20	$160.20
Purchase #6	$97.33	9.693%	$106.7642	$106.76	$106.75	$106.80
Purchase #7	$79.45	3.724%	$82.4087	$82.41	$82.40	$82.40
7 purchase totals =	$835.54		$903.4817	$903.47	$903.45	$903.50