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	$25.59	13.163%	$28.9584	$28.96	$28.95	$29.00
Purchase #2	$59.75	12.541%	$67.2432	$67.24	$67.25	$67.20
Purchase #3	$28.81	9.496%	$31.5458	$31.55	$31.55	$31.50
Purchase #4	$101.35	5.662%	$107.0884	$107.09	$107.10	$107.10
Purchase #5	$97.25	3.708%	$100.856	$100.86	$100.85	$100.90
Purchase #6	$171.59	11.472%	$191.2748	$191.27	$191.25	$191.30
Purchase #7	$71.74	8.721%	$77.9964	$78.00	$78.00	$78.00
7 purchase totals =	$556.08		$604.9630	$604.97	$604.95	$605.00