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	$99.55	11.526%	$111.0241	$111.02	$111.00	$111.00
Purchase #2	$193.87	5.482%	$204.498	$204.50	$204.50	$204.50
Purchase #3	$52.47	6.276%	$55.763	$55.76	$55.75	$55.80
Purchase #4	$36.73	12.549%	$41.3392	$41.34	$41.35	$41.30
Purchase #5	$180.94	9.848%	$198.759	$198.76	$198.75	$198.80
Purchase #6	$116.31	4.433%	$121.466	$121.47	$121.45	$121.50
Purchase #7	$76.40	8.227%	$82.6854	$82.69	$82.70	$82.70
7 purchase totals =	$756.27		$815.5347	$815.54	$815.50	$815.60