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	$24.61	13.613%	$27.9602	$27.96	$27.95	$28.00
Purchase #2	$10.86	10.522%	$12.0027	$12.00	$12.00	$12.00
Purchase #3	$84.30	6.240%	$89.5603	$89.56	$89.55	$89.60
Purchase #4	$185.58	6.420%	$197.4942	$197.49	$197.50	$197.50
Purchase #5	$24.64	5.107%	$25.8984	$25.90	$25.90	$25.90
Purchase #6	$101.83	10.804%	$112.8317	$112.83	$112.85	$112.80
Purchase #7	$128.37	12.442%	$144.3418	$144.34	$144.35	$144.30
7 purchase totals =	$560.19		$610.0893	$610.08	$610.10	$610.10