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	$181.34	6.666%	$193.4281	$193.43	$193.45	$193.40
Purchase #2	$158.61	10.556%	$175.3529	$175.35	$175.35	$175.40
Purchase #3	$156.55	10.331%	$172.7232	$172.72	$172.70	$172.70
Purchase #4	$58.80	4.580%	$61.493	$61.49	$61.50	$61.50
Purchase #5	$65.45	12.558%	$73.6692	$73.67	$73.65	$73.70
Purchase #6	$57.62	9.161%	$62.8986	$62.90	$62.90	$62.90
Purchase #7	$240.32	13.380%	$272.4748	$272.47	$272.45	$272.50
7 purchase totals =	$918.69		$1,012.0398	$1,012.03	$1,012.00	$1,012.10