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	$170.58	3.659%	$176.8215	$176.82	$176.80	$176.80
Purchase #2	$110.35	8.583%	$119.8213	$119.82	$119.80	$119.80
Purchase #3	$192.53	5.664%	$203.4349	$203.43	$203.45	$203.40
Purchase #4	$153.75	13.352%	$174.2787	$174.28	$174.30	$174.30
Purchase #5	$53.50	6.589%	$57.0251	$57.03	$57.05	$57.00
Purchase #6	$151.46	8.761%	$164.7294	$164.73	$164.75	$164.70
Purchase #7	$98.29	13.484%	$111.5434	$111.54	$111.55	$111.50
7 purchase totals =	$930.46		$1,007.6543	$1,007.65	$1,007.70	$1,007.50