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	$153.89	3.240%	$158.876	$158.88	$158.90	$158.90
Purchase #2	$137.27	9.485%	$150.2901	$150.29	$150.30	$150.30
Purchase #3	$134.27	6.254%	$142.6672	$142.67	$142.65	$142.70
Purchase #4	$111.85	9.264%	$122.2118	$122.21	$122.20	$122.20
Purchase #5	$75.32	4.516%	$78.7215	$78.72	$78.70	$78.70
Purchase #6	$140.30	13.398%	$159.0974	$159.10	$159.10	$159.10
Purchase #7	$93.35	5.340%	$98.3349	$98.33	$98.35	$98.30
7 purchase totals =	$846.25		$910.1989	$910.20	$910.20	$910.20