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	$28.78	13.438%	$32.6475	$32.65	$32.65	$32.60
Purchase #2	$97.41	5.714%	$102.976	$102.98	$103.00	$103.00
Purchase #3	$65.35	7.355%	$70.1565	$70.16	$70.15	$70.20
Purchase #4	$48.38	6.677%	$51.6103	$51.61	$51.60	$51.60
Purchase #5	$41.30	9.630%	$45.2772	$45.28	$45.30	$45.30
Purchase #6	$93.48	3.235%	$96.5041	$96.50	$96.50	$96.50
Purchase #7	$146.89	13.534%	$166.7701	$166.77	$166.75	$166.80
7 purchase totals =	$521.59		$565.9417	$565.95	$565.95	$566.00