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	$227.32	11.376%	$253.1799	$253.18	$253.20	$253.20
Purchase #2	$43.62	4.520%	$45.5916	$45.59	$45.60	$45.60
Purchase #3	$68.35	13.442%	$77.5376	$77.54	$77.55	$77.50
Purchase #4	$29.72	4.106%	$30.9403	$30.94	$30.95	$30.90
Purchase #5	$99.78	5.551%	$105.3188	$105.32	$105.30	$105.30
Purchase #6	$152.93	10.227%	$168.5702	$168.57	$168.55	$168.60
Purchase #7	$72.40	12.681%	$81.581	$81.58	$81.60	$81.60
7 purchase totals =	$694.12		$762.7194	$762.72	$762.75	$762.70