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	$44.97	10.473%	$49.6797	$49.68	$49.70	$49.70
Purchase #2	$112.69	6.129%	$119.5968	$119.60	$119.60	$119.60
Purchase #3	$185.69	10.723%	$205.6015	$205.60	$205.60	$205.60
Purchase #4	$195.93	4.695%	$205.1289	$205.13	$205.15	$205.10
Purchase #5	$128.31	8.760%	$139.55	$139.55	$139.55	$139.60
Purchase #6	$56.40	4.847%	$59.1337	$59.13	$59.15	$59.10
Purchase #7	$10.98	10.698%	$12.1546	$12.15	$12.15	$12.20
7 purchase totals =	$734.97		$790.8452	$790.84	$790.90	$790.90