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	$11.42	3.751%	$11.8484	$11.85	$11.85	$11.80
Purchase #2	$225.92	10.348%	$249.2982	$249.30	$249.30	$249.30
Purchase #3	$86.82	4.183%	$90.4517	$90.45	$90.45	$90.50
Purchase #4	$22.81	4.619%	$23.8636	$23.86	$23.85	$23.90
Purchase #5	$164.94	13.839%	$187.766	$187.77	$187.75	$187.80
Purchase #6	$250.32	11.620%	$279.4072	$279.41	$279.40	$279.40
Purchase #7	$200.46	10.806%	$222.1217	$222.12	$222.10	$222.10
7 purchase totals =	$962.69		$1,064.7568	$1,064.76	$1,064.70	$1,064.80