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	$83.36	8.462%	$90.4139	$90.41	$90.40	$90.40
Purchase #2	$222.71	10.450%	$245.9832	$245.98	$246.00	$246.00
Purchase #3	$63.61	10.265%	$70.1396	$70.14	$70.15	$70.10
Purchase #4	$114.27	6.533%	$121.7353	$121.74	$121.75	$121.70
Purchase #5	$56.59	4.575%	$59.179	$59.18	$59.20	$59.20
Purchase #6	$160.28	13.218%	$181.4658	$181.47	$181.45	$181.50
Purchase #7	$108.93	8.758%	$118.4701	$118.47	$118.45	$118.50
7 purchase totals =	$809.75		$887.3869	$887.39	$887.40	$887.40