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	$27.93	4.723%	$29.2491	$29.25	$29.25	$29.20
Purchase #2	$63.45	5.341%	$66.8389	$66.84	$66.85	$66.80
Purchase #3	$89.84	11.801%	$100.442	$100.44	$100.45	$100.40
Purchase #4	$129.69	6.274%	$137.8268	$137.83	$137.85	$137.80
Purchase #5	$97.27	5.813%	$102.9243	$102.92	$102.90	$102.90
Purchase #6	$184.60	4.556%	$193.0104	$193.01	$193.00	$193.00
Purchase #7	$128.73	11.588%	$143.6472	$143.65	$143.65	$143.60
7 purchase totals =	$721.51		$773.9387	$773.94	$773.95	$773.70