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	$11.51	4.287%	$12.0034	$12.00	$12.00	$12.00
Purchase #2	$50.67	6.371%	$53.8982	$53.90	$53.90	$53.90
Purchase #3	$97.97	7.488%	$105.306	$105.31	$105.30	$105.30
Purchase #4	$78.47	9.165%	$85.6618	$85.66	$85.65	$85.70
Purchase #5	$173.84	5.661%	$183.6811	$183.68	$183.70	$183.70
Purchase #6	$40.69	9.585%	$44.5901	$44.59	$44.60	$44.60
Purchase #7	$80.30	12.326%	$90.1978	$90.20	$90.20	$90.20
7 purchase totals =	$533.45		$575.3384	$575.34	$575.35	$575.40