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	$20.82	11.581%	$23.2312	$23.23	$23.25	$23.20
Purchase #2	$51.94	7.198%	$55.6786	$55.68	$55.70	$55.70
Purchase #3	$56.97	3.721%	$59.0899	$59.09	$59.10	$59.10
Purchase #4	$161.37	10.621%	$178.5091	$178.51	$178.50	$178.50
Purchase #5	$241.44	11.846%	$270.041	$270.04	$270.05	$270.00
Purchase #6	$93.59	10.557%	$103.4703	$103.47	$103.45	$103.50
Purchase #7	$233.56	4.414%	$243.8693	$243.87	$243.85	$243.90
7 purchase totals =	$859.69		$933.8894	$933.89	$933.90	$933.90