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	$150.78	6.459%	$160.5189	$160.52	$160.50	$160.50
Purchase #2	$215.63	4.200%	$224.6865	$224.69	$224.70	$224.70
Purchase #3	$98.29	13.749%	$111.8039	$111.80	$111.80	$111.80
Purchase #4	$154.61	6.196%	$164.1896	$164.19	$164.20	$164.20
Purchase #5	$155.61	13.424%	$176.4991	$176.50	$176.50	$176.50
Purchase #6	$16.33	5.188%	$17.1772	$17.18	$17.20	$17.20
Purchase #7	$78.40	6.286%	$83.3282	$83.33	$83.35	$83.30
7 purchase totals =	$869.65		$938.2034	$938.21	$938.25	$938.20