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	$144.68	13.410%	$164.0816	$164.08	$164.10	$164.10
Purchase #2	$85.87	4.378%	$89.6294	$89.63	$89.65	$89.60
Purchase #3	$139.97	5.261%	$147.3338	$147.33	$147.35	$147.30
Purchase #4	$73.46	6.177%	$77.9976	$78.00	$78.00	$78.00
Purchase #5	$76.60	9.388%	$83.7912	$83.79	$83.80	$83.80
Purchase #6	$137.70	10.151%	$151.6779	$151.68	$151.70	$151.70
Purchase #7	$176.25	11.460%	$196.4483	$196.45	$196.45	$196.40
7 purchase totals =	$834.53		$910.9598	$910.96	$911.05	$910.90