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	$39.29	9.773%	$43.1298	$43.13	$43.15	$43.10
Purchase #2	$237.79	7.854%	$256.466	$256.47	$256.45	$256.50
Purchase #3	$40.80	11.856%	$45.6372	$45.64	$45.65	$45.60
Purchase #4	$151.92	10.201%	$167.4174	$167.42	$167.40	$167.40
Purchase #5	$52.33	4.711%	$54.7953	$54.80	$54.80	$54.80
Purchase #6	$246.99	6.671%	$263.4667	$263.47	$263.45	$263.50
Purchase #7	$195.39	6.662%	$208.4069	$208.41	$208.40	$208.40
7 purchase totals =	$964.51		$1,039.3193	$1,039.34	$1,039.30	$1,039.30