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	$41.28	4.496%	$43.1359	$43.14	$43.15	$43.10
Purchase #2	$60.86	12.348%	$68.375	$68.38	$68.40	$68.40
Purchase #3	$214.32	13.601%	$243.4697	$243.47	$243.45	$243.50
Purchase #4	$173.28	9.367%	$189.5111	$189.51	$189.50	$189.50
Purchase #5	$18.33	3.411%	$18.9552	$18.96	$18.95	$19.00
Purchase #6	$41.88	3.544%	$43.3642	$43.36	$43.35	$43.40
Purchase #7	$30.53	5.105%	$32.0886	$32.09	$32.10	$32.10
7 purchase totals =	$580.48		$638.8997	$638.91	$638.90	$639.00