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	$204.98	13.821%	$233.3103	$233.31	$233.30	$233.30
Purchase #2	$68.69	12.699%	$77.4129	$77.41	$77.40	$77.40
Purchase #3	$140.94	13.433%	$159.8725	$159.87	$159.85	$159.90
Purchase #4	$164.58	3.617%	$170.5329	$170.53	$170.55	$170.50
Purchase #5	$198.89	4.642%	$208.1225	$208.12	$208.10	$208.10
Purchase #6	$101.96	11.408%	$113.5916	$113.59	$113.60	$113.60
Purchase #7	$126.47	8.818%	$137.6221	$137.62	$137.60	$137.60
7 purchase totals =	$1,006.51		$1,100.4648	$1,100.45	$1,100.40	$1,100.40