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	$25.70	11.148%	$28.565	$28.57	$28.55	$28.60
Purchase #2	$103.50	10.718%	$114.5931	$114.59	$114.60	$114.60
Purchase #3	$64.81	12.232%	$72.7376	$72.74	$72.75	$72.70
Purchase #4	$65.66	4.831%	$68.832	$68.83	$68.85	$68.80
Purchase #5	$72.44	9.672%	$79.4464	$79.45	$79.45	$79.40
Purchase #6	$130.38	12.722%	$146.9669	$146.97	$146.95	$147.00
Purchase #7	$138.78	10.864%	$153.8571	$153.86	$153.85	$153.90
7 purchase totals =	$601.27		$664.9981	$665.01	$665.00	$665.00