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	$5.80	5.780%	$6.1352	$6.14	$6.15	$6.10
Purchase #2	$35.69	4.292%	$37.2218	$37.22	$37.20	$37.20
Purchase #3	$114.26	13.371%	$129.5377	$129.54	$129.55	$129.50
Purchase #4	$29.85	8.792%	$32.4744	$32.47	$32.45	$32.50
Purchase #5	$171.61	13.351%	$194.5217	$194.52	$194.50	$194.50
Purchase #6	$163.78	3.155%	$168.9473	$168.95	$168.95	$168.90
Purchase #7	$140.40	7.260%	$150.593	$150.59	$150.60	$150.60
7 purchase totals =	$661.39		$719.4311	$719.43	$719.40	$719.30