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	$145.85	6.516%	$155.3536	$155.35	$155.35	$155.40
Purchase #2	$100.42	10.625%	$111.0896	$111.09	$111.10	$111.10
Purchase #3	$245.42	13.583%	$278.7554	$278.76	$278.75	$278.80
Purchase #4	$72.39	8.368%	$78.4476	$78.45	$78.45	$78.40
Purchase #5	$189.66	3.634%	$196.5522	$196.55	$196.55	$196.60
Purchase #6	$208.33	5.554%	$219.9006	$219.90	$219.90	$219.90
Purchase #7	$211.73	11.270%	$235.592	$235.59	$235.60	$235.60
7 purchase totals =	$1,173.80		$1,275.6910	$1,275.69	$1,275.70	$1,275.80