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	$13.79	10.834%	$15.284	$15.28	$15.30	$15.30
Purchase #2	$247.72	4.627%	$259.182	$259.18	$259.20	$259.20
Purchase #3	$59.76	10.175%	$65.8406	$65.84	$65.85	$65.80
Purchase #4	$175.77	6.570%	$187.3181	$187.32	$187.30	$187.30
Purchase #5	$119.57	9.176%	$130.5417	$130.54	$130.55	$130.50
Purchase #6	$123.72	8.232%	$133.9046	$133.90	$133.90	$133.90
Purchase #7	$27.58	3.302%	$28.4907	$28.49	$28.50	$28.50
7 purchase totals =	$767.91		$820.5617	$820.55	$820.60	$820.50