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	$141.45	3.557%	$146.4814	$146.48	$146.50	$146.50
Purchase #2	$97.55	7.799%	$105.1579	$105.16	$105.15	$105.20
Purchase #3	$71.56	3.854%	$74.3179	$74.32	$74.30	$74.30
Purchase #4	$171.82	10.183%	$189.3164	$189.32	$189.30	$189.30
Purchase #5	$105.36	5.152%	$110.7881	$110.79	$110.80	$110.80
Purchase #6	$153.52	8.654%	$166.8056	$166.81	$166.80	$166.80
Purchase #7	$77.59	10.808%	$85.9759	$85.98	$86.00	$86.00
7 purchase totals =	$818.85		$878.8432	$878.86	$878.85	$878.90