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	$93.87	6.404%	$99.8814	$99.88	$99.90	$99.90
Purchase #2	$145.92	11.606%	$162.8555	$162.86	$162.85	$162.90
Purchase #3	$101.35	13.391%	$114.9218	$114.92	$114.90	$114.90
Purchase #4	$123.45	10.702%	$136.6616	$136.66	$136.65	$136.70
Purchase #5	$113.53	12.371%	$127.5748	$127.57	$127.55	$127.60
Purchase #6	$187.45	5.314%	$197.4111	$197.41	$197.40	$197.40
Purchase #7	$21.95	9.516%	$24.0388	$24.04	$24.05	$24.00
7 purchase totals =	$787.52		$863.3450	$863.34	$863.30	$863.40