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	$25.92	10.292%	$28.5877	$28.59	$28.60	$28.60
Purchase #2	$69.56	13.462%	$78.9242	$78.92	$78.90	$78.90
Purchase #3	$16.39	5.103%	$17.2264	$17.23	$17.25	$17.20
Purchase #4	$170.86	5.169%	$179.6918	$179.69	$179.70	$179.70
Purchase #5	$223.84	11.484%	$249.5458	$249.55	$249.55	$249.50
Purchase #6	$9.86	6.758%	$10.5263	$10.53	$10.55	$10.50
Purchase #7	$141.96	5.848%	$150.2618	$150.26	$150.25	$150.30
7 purchase totals =	$658.39		$714.7640	$714.77	$714.80	$714.70