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	$53.84	10.326%	$59.3995	$59.40	$59.40	$59.40
Purchase #2	$154.66	5.198%	$162.6992	$162.70	$162.70	$162.70
Purchase #3	$243.54	9.632%	$266.9978	$267.00	$267.00	$267.00
Purchase #4	$138.94	8.765%	$151.1181	$151.12	$151.10	$151.10
Purchase #5	$84.71	6.695%	$90.3813	$90.38	$90.40	$90.40
Purchase #6	$76.34	9.490%	$83.5847	$83.58	$83.60	$83.60
Purchase #7	$19.27	9.719%	$21.1429	$21.14	$21.15	$21.10
7 purchase totals =	$771.30		$835.3235	$835.32	$835.35	$835.30