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	$178.73	11.683%	$199.611	$199.61	$199.60	$199.60
Purchase #2	$141.69	8.642%	$153.9348	$153.93	$153.95	$153.90
Purchase #3	$145.75	6.709%	$155.5284	$155.53	$155.55	$155.50
Purchase #4	$55.38	4.601%	$57.928	$57.93	$57.95	$57.90
Purchase #5	$133.89	8.571%	$145.3657	$145.37	$145.35	$145.40
Purchase #6	$88.80	11.759%	$99.242	$99.24	$99.25	$99.20
Purchase #7	$105.51	5.795%	$111.6243	$111.62	$111.60	$111.60
7 purchase totals =	$849.75		$923.2342	$923.23	$923.25	$923.10