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	$136.28	13.276%	$154.3725	$154.37	$154.35	$154.40
Purchase #2	$148.85	12.500%	$167.4563	$167.46	$167.45	$167.50
Purchase #3	$26.54	6.453%	$28.2526	$28.25	$28.25	$28.30
Purchase #4	$20.81	5.517%	$21.9581	$21.96	$21.95	$22.00
Purchase #5	$74.69	5.616%	$78.8846	$78.88	$78.90	$78.90
Purchase #6	$175.29	11.624%	$195.6657	$195.67	$195.65	$195.70
Purchase #7	$133.79	4.596%	$139.939	$139.94	$139.95	$139.90
7 purchase totals =	$716.25		$786.5288	$786.53	$786.50	$786.70