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	$7.43	8.778%	$8.0822	$8.08	$8.10	$8.10
Purchase #2	$129.37	11.311%	$144.003	$144.00	$144.00	$144.00
Purchase #3	$30.40	8.678%	$33.0381	$33.04	$33.05	$33.00
Purchase #4	$196.30	6.194%	$208.4588	$208.46	$208.45	$208.50
Purchase #5	$125.67	9.352%	$137.4227	$137.42	$137.40	$137.40
Purchase #6	$140.63	3.121%	$145.0191	$145.02	$145.00	$145.00
Purchase #7	$105.90	5.269%	$111.4799	$111.48	$111.50	$111.50
7 purchase totals =	$735.70		$787.5038	$787.50	$787.50	$787.50