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	$19.90	4.465%	$20.7885	$20.79	$20.80	$20.80
Purchase #2	$52.65	12.461%	$59.2107	$59.21	$59.20	$59.20
Purchase #3	$176.34	11.161%	$196.0213	$196.02	$196.00	$196.00
Purchase #4	$92.35	11.549%	$103.0155	$103.02	$103.00	$103.00
Purchase #5	$21.85	5.329%	$23.0144	$23.01	$23.00	$23.00
Purchase #6	$69.76	7.249%	$74.8169	$74.82	$74.80	$74.80
Purchase #7	$18.68	4.712%	$19.5602	$19.56	$19.55	$19.60
7 purchase totals =	$451.53		$496.4275	$496.43	$496.35	$496.40