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	$89.71	13.808%	$102.0972	$102.10	$102.10	$102.10
Purchase #2	$34.82	6.702%	$37.1536	$37.15	$37.15	$37.20
Purchase #3	$26.25	10.528%	$29.0136	$29.01	$29.00	$29.00
Purchase #4	$166.60	11.566%	$185.869	$185.87	$185.85	$185.90
Purchase #5	$45.29	10.139%	$49.882	$49.88	$49.90	$49.90
Purchase #6	$151.92	9.333%	$166.0987	$166.10	$166.10	$166.10
Purchase #7	$142.98	6.505%	$152.2808	$152.28	$152.30	$152.30
7 purchase totals =	$657.57		$722.3949	$722.39	$722.40	$722.50