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	$233.90	9.653%	$256.4784	$256.48	$256.50	$256.50
Purchase #2	$16.35	5.456%	$17.2421	$17.24	$17.25	$17.20
Purchase #3	$67.33	11.620%	$75.1537	$75.15	$75.15	$75.20
Purchase #4	$136.99	5.187%	$144.0957	$144.10	$144.10	$144.10
Purchase #5	$218.88	9.123%	$238.8484	$238.85	$238.85	$238.80
Purchase #6	$80.69	12.298%	$90.6133	$90.61	$90.60	$90.60
Purchase #7	$62.62	8.147%	$67.7217	$67.72	$67.70	$67.70
7 purchase totals =	$816.76		$890.1533	$890.15	$890.15	$890.10