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	$19.41	13.283%	$21.9882	$21.99	$22.00	$22.00
Purchase #2	$237.37	8.159%	$256.737	$256.74	$256.75	$256.70
Purchase #3	$88.85	13.467%	$100.8154	$100.82	$100.80	$100.80
Purchase #4	$214.35	12.392%	$240.9123	$240.91	$240.90	$240.90
Purchase #5	$239.25	8.665%	$259.981	$259.98	$260.00	$260.00
Purchase #6	$51.72	3.220%	$53.3854	$53.39	$53.40	$53.40
Purchase #7	$154.81	7.188%	$165.9377	$165.94	$165.95	$165.90
7 purchase totals =	$1,005.76		$1,099.7570	$1,099.77	$1,099.80	$1,099.70