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	$151.26	3.560%	$156.6449	$156.64	$156.65	$156.60
Purchase #2	$140.52	8.396%	$152.3181	$152.32	$152.30	$152.30
Purchase #3	$29.54	9.305%	$32.2887	$32.29	$32.30	$32.30
Purchase #4	$217.26	9.617%	$238.1539	$238.15	$238.15	$238.20
Purchase #5	$45.39	7.577%	$48.8292	$48.83	$48.85	$48.80
Purchase #6	$168.30	5.777%	$178.0227	$178.02	$178.00	$178.00
Purchase #7	$98.73	9.741%	$108.3473	$108.35	$108.35	$108.30
7 purchase totals =	$851.00		$914.6048	$914.60	$914.60	$914.50