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	$15.66	11.871%	$17.519	$17.52	$17.50	$17.50
Purchase #2	$96.61	12.636%	$108.8176	$108.82	$108.80	$108.80
Purchase #3	$212.31	3.432%	$219.5965	$219.60	$219.60	$219.60
Purchase #4	$160.74	4.753%	$168.38	$168.38	$168.40	$168.40
Purchase #5	$90.59	11.395%	$100.9127	$100.91	$100.90	$100.90
Purchase #6	$167.36	13.719%	$190.3201	$190.32	$190.30	$190.30
Purchase #7	$134.71	12.269%	$151.2376	$151.24	$151.25	$151.20
7 purchase totals =	$877.98		$956.7835	$956.79	$956.75	$956.70