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	$7.75	11.540%	$8.6444	$8.64	$8.65	$8.60
Purchase #2	$239.54	11.366%	$266.7661	$266.77	$266.75	$266.80
Purchase #3	$76.94	8.514%	$83.4907	$83.49	$83.50	$83.50
Purchase #4	$120.83	11.265%	$134.4415	$134.44	$134.45	$134.40
Purchase #5	$48.82	9.282%	$53.3515	$53.35	$53.35	$53.40
Purchase #6	$216.35	5.205%	$227.611	$227.61	$227.60	$227.60
Purchase #7	$75.41	9.597%	$82.6471	$82.65	$82.65	$82.60
7 purchase totals =	$785.64		$856.9523	$856.95	$856.95	$856.90