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	$30.58	6.452%	$32.553	$32.55	$32.55	$32.60
Purchase #2	$90.89	6.284%	$96.6015	$96.60	$96.60	$96.60
Purchase #3	$40.68	3.621%	$42.153	$42.15	$42.15	$42.20
Purchase #4	$125.32	11.241%	$139.4072	$139.41	$139.40	$139.40
Purchase #5	$202.98	5.574%	$214.2941	$214.29	$214.30	$214.30
Purchase #6	$176.84	7.789%	$190.6141	$190.61	$190.60	$190.60
Purchase #7	$161.38	5.244%	$169.8428	$169.84	$169.85	$169.80
7 purchase totals =	$828.67		$885.4657	$885.45	$885.45	$885.50