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	$100.75	6.285%	$107.0821	$107.08	$107.10	$107.10
Purchase #2	$108.41	10.150%	$119.4136	$119.41	$119.40	$119.40
Purchase #3	$168.86	5.659%	$178.4158	$178.42	$178.40	$178.40
Purchase #4	$61.69	9.150%	$67.3346	$67.33	$67.35	$67.30
Purchase #5	$101.74	3.172%	$104.9672	$104.97	$104.95	$105.00
Purchase #6	$86.32	4.515%	$90.2173	$90.22	$90.20	$90.20
Purchase #7	$232.62	6.685%	$248.1706	$248.17	$248.15	$248.20
7 purchase totals =	$860.39		$915.6012	$915.60	$915.55	$915.60