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	$142.77	12.340%	$160.3878	$160.39	$160.40	$160.40
Purchase #2	$85.64	6.191%	$90.942	$90.94	$90.95	$90.90
Purchase #3	$50.80	12.352%	$57.0748	$57.07	$57.05	$57.10
Purchase #4	$90.68	5.709%	$95.8569	$95.86	$95.85	$95.90
Purchase #5	$176.75	13.287%	$200.2348	$200.23	$200.25	$200.20
Purchase #6	$151.52	3.500%	$156.8232	$156.82	$156.80	$156.80
Purchase #7	$64.59	12.862%	$72.8976	$72.90	$72.90	$72.90
7 purchase totals =	$762.75		$834.2171	$834.21	$834.20	$834.20