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	$133.43	7.636%	$143.6187	$143.62	$143.60	$143.60
Purchase #2	$217.68	13.363%	$246.7686	$246.77	$246.75	$246.80
Purchase #3	$39.31	10.790%	$43.5515	$43.55	$43.55	$43.60
Purchase #4	$90.85	5.572%	$95.9122	$95.91	$95.90	$95.90
Purchase #5	$92.47	11.807%	$103.3879	$103.39	$103.40	$103.40
Purchase #6	$151.58	10.600%	$167.6475	$167.65	$167.65	$167.60
Purchase #7	$30.71	10.257%	$33.8599	$33.86	$33.85	$33.90
7 purchase totals =	$756.03		$834.7463	$834.75	$834.70	$834.80