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	$99.96	12.658%	$112.6129	$112.61	$112.60	$112.60
Purchase #2	$85.51	6.241%	$90.8467	$90.85	$90.85	$90.80
Purchase #3	$128.38	13.846%	$146.1555	$146.16	$146.15	$146.20
Purchase #4	$65.69	6.335%	$69.8515	$69.85	$69.85	$69.90
Purchase #5	$102.86	7.455%	$110.5282	$110.53	$110.55	$110.50
Purchase #6	$126.91	7.160%	$135.9968	$136.00	$136.00	$136.00
Purchase #7	$145.92	4.321%	$152.2252	$152.23	$152.25	$152.20
7 purchase totals =	$755.23		$818.2168	$818.23	$818.25	$818.20