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	$169.25	10.198%	$186.5101	$186.51	$186.50	$186.50
Purchase #2	$75.75	13.386%	$85.8899	$85.89	$85.90	$85.90
Purchase #3	$104.69	12.191%	$117.4528	$117.45	$117.45	$117.50
Purchase #4	$154.73	12.498%	$174.0682	$174.07	$174.05	$174.10
Purchase #5	$248.95	8.697%	$270.6012	$270.60	$270.60	$270.60
Purchase #6	$50.69	3.510%	$52.4692	$52.47	$52.45	$52.50
Purchase #7	$125.55	5.660%	$132.6561	$132.66	$132.65	$132.70
7 purchase totals =	$929.61		$1,019.6475	$1,019.65	$1,019.60	$1,019.80