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	$37.72	3.830%	$39.1647	$39.16	$39.15	$39.20
Purchase #2	$146.30	4.525%	$152.9201	$152.92	$152.90	$152.90
Purchase #3	$7.28	4.243%	$7.5889	$7.59	$7.60	$7.60
Purchase #4	$213.46	8.457%	$231.5123	$231.51	$231.50	$231.50
Purchase #5	$35.79	3.603%	$37.0795	$37.08	$37.10	$37.10
Purchase #6	$61.41	4.868%	$64.3994	$64.40	$64.40	$64.40
Purchase #7	$151.89	6.546%	$161.8327	$161.83	$161.85	$161.80
7 purchase totals =	$653.85		$694.4976	$694.49	$694.50	$694.50