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	$139.48	11.781%	$155.9121	$155.91	$155.90	$155.90
Purchase #2	$31.47	12.658%	$35.4535	$35.45	$35.45	$35.50
Purchase #3	$103.90	12.433%	$116.8179	$116.82	$116.80	$116.80
Purchase #4	$187.32	9.167%	$204.4916	$204.49	$204.50	$204.50
Purchase #5	$5.98	13.275%	$6.7738	$6.77	$6.75	$6.80
Purchase #6	$53.50	9.519%	$58.5927	$58.59	$58.60	$58.60
Purchase #7	$57.52	6.837%	$61.4526	$61.45	$61.45	$61.50
7 purchase totals =	$579.17		$639.4942	$639.48	$639.45	$639.60