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	$111.48	11.803%	$124.638	$124.64	$124.65	$124.60
Purchase #2	$173.85	4.574%	$181.8019	$181.80	$181.80	$181.80
Purchase #3	$228.47	5.678%	$241.4425	$241.44	$241.45	$241.40
Purchase #4	$92.88	13.630%	$105.5395	$105.54	$105.55	$105.50
Purchase #5	$78.63	3.215%	$81.158	$81.16	$81.15	$81.20
Purchase #6	$64.55	12.320%	$72.5026	$72.50	$72.50	$72.50
Purchase #7	$11.94	6.250%	$12.6863	$12.69	$12.70	$12.70
7 purchase totals =	$761.80		$819.7688	$819.77	$819.80	$819.70