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	$28.26	9.116%	$30.8362	$30.84	$30.85	$30.80
Purchase #2	$184.94	7.274%	$198.3925	$198.39	$198.40	$198.40
Purchase #3	$176.61	6.291%	$187.7205	$187.72	$187.70	$187.70
Purchase #4	$245.69	5.181%	$258.4192	$258.42	$258.40	$258.40
Purchase #5	$173.92	13.200%	$196.8774	$196.88	$196.90	$196.90
Purchase #6	$232.79	11.273%	$259.0324	$259.03	$259.05	$259.00
Purchase #7	$81.95	10.797%	$90.7981	$90.80	$90.80	$90.80
7 purchase totals =	$1,124.16		$1,222.0763	$1,222.08	$1,222.10	$1,222.00