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	$144.92	13.705%	$164.7813	$164.78	$164.80	$164.80
Purchase #2	$173.38	6.731%	$185.0502	$185.05	$185.05	$185.10
Purchase #3	$87.60	9.562%	$95.9763	$95.98	$96.00	$96.00
Purchase #4	$22.73	8.124%	$24.5766	$24.58	$24.60	$24.60
Purchase #5	$142.99	6.847%	$152.7805	$152.78	$152.80	$152.80
Purchase #6	$191.80	4.386%	$200.2123	$200.21	$200.20	$200.20
Purchase #7	$147.77	4.609%	$154.5807	$154.58	$154.60	$154.60
7 purchase totals =	$911.19		$977.9579	$977.96	$978.05	$978.10