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	$58.63	13.854%	$66.7526	$66.75	$66.75	$66.80
Purchase #2	$165.63	12.189%	$185.8186	$185.82	$185.80	$185.80
Purchase #3	$39.46	11.190%	$43.8756	$43.88	$43.90	$43.90
Purchase #4	$173.76	5.367%	$183.0857	$183.09	$183.10	$183.10
Purchase #5	$78.32	4.673%	$81.9799	$81.98	$82.00	$82.00
Purchase #6	$39.87	4.471%	$41.6526	$41.65	$41.65	$41.70
Purchase #7	$180.43	13.193%	$204.2341	$204.23	$204.25	$204.20
7 purchase totals =	$736.10		$807.3991	$807.40	$807.45	$807.50