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	$146.78	9.620%	$160.9002	$160.90	$160.90	$160.90
Purchase #2	$29.84	7.730%	$32.1466	$32.15	$32.15	$32.10
Purchase #3	$203.90	6.826%	$217.8182	$217.82	$217.80	$217.80
Purchase #4	$157.31	6.272%	$167.1765	$167.18	$167.20	$167.20
Purchase #5	$230.95	4.856%	$242.1649	$242.16	$242.15	$242.20
Purchase #6	$119.72	10.753%	$132.5935	$132.59	$132.60	$132.60
Purchase #7	$156.55	5.638%	$165.3763	$165.38	$165.40	$165.40
7 purchase totals =	$1,045.05		$1,118.1762	$1,118.18	$1,118.20	$1,118.20