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	$49.43	10.409%	$54.5752	$54.58	$54.60	$54.60
Purchase #2	$152.51	12.480%	$171.5432	$171.54	$171.55	$171.50
Purchase #3	$209.95	10.267%	$231.5056	$231.51	$231.50	$231.50
Purchase #4	$124.51	3.828%	$129.2762	$129.28	$129.30	$129.30
Purchase #5	$17.69	5.184%	$18.607	$18.61	$18.60	$18.60
Purchase #6	$90.51	5.464%	$95.4555	$95.46	$95.45	$95.50
Purchase #7	$155.32	5.501%	$163.8642	$163.86	$163.85	$163.90
7 purchase totals =	$799.92		$864.8269	$864.84	$864.85	$864.90