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	$130.59	10.644%	$144.49	$144.49	$144.50	$144.50
Purchase #2	$147.46	8.793%	$160.4262	$160.43	$160.45	$160.40
Purchase #3	$144.66	6.149%	$153.5551	$153.56	$153.55	$153.60
Purchase #4	$157.64	6.236%	$167.4704	$167.47	$167.45	$167.50
Purchase #5	$110.78	4.504%	$115.7695	$115.77	$115.75	$115.80
Purchase #6	$105.87	13.284%	$119.9338	$119.93	$119.95	$119.90
Purchase #7	$36.54	3.825%	$37.9377	$37.94	$37.95	$37.90
7 purchase totals =	$833.54		$899.5827	$899.59	$899.60	$899.60