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	$29.78	10.491%	$32.9042	$32.90	$32.90	$32.90
Purchase #2	$93.52	3.458%	$96.7539	$96.75	$96.75	$96.80
Purchase #3	$35.31	11.364%	$39.3226	$39.32	$39.30	$39.30
Purchase #4	$156.38	7.503%	$168.1132	$168.11	$168.10	$168.10
Purchase #5	$21.64	5.450%	$22.8194	$22.82	$22.80	$22.80
Purchase #6	$152.60	13.725%	$173.5444	$173.54	$173.55	$173.50
Purchase #7	$33.93	4.266%	$35.3775	$35.38	$35.40	$35.40
7 purchase totals =	$523.16		$568.8352	$568.82	$568.80	$568.80