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	$156.75	5.404%	$165.2208	$165.22	$165.20	$165.20
Purchase #2	$16.75	6.330%	$17.8103	$17.81	$17.80	$17.80
Purchase #3	$72.58	10.677%	$80.3294	$80.33	$80.35	$80.30
Purchase #4	$46.60	12.746%	$52.5396	$52.54	$52.55	$52.50
Purchase #5	$204.25	9.337%	$223.3208	$223.32	$223.30	$223.30
Purchase #6	$113.79	12.116%	$127.5768	$127.58	$127.60	$127.60
Purchase #7	$241.85	10.437%	$267.0919	$267.09	$267.10	$267.10
7 purchase totals =	$852.57		$933.8896	$933.89	$933.90	$933.80