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	$33.40	3.153%	$34.4531	$34.45	$34.45	$34.50
Purchase #2	$115.86	13.167%	$131.1153	$131.12	$131.10	$131.10
Purchase #3	$33.34	13.831%	$37.9513	$37.95	$37.95	$38.00
Purchase #4	$146.60	3.198%	$151.2883	$151.29	$151.30	$151.30
Purchase #5	$186.44	7.619%	$200.6449	$200.64	$200.65	$200.60
Purchase #6	$27.83	6.172%	$29.5477	$29.55	$29.55	$29.50
Purchase #7	$93.55	5.339%	$98.5446	$98.54	$98.55	$98.50
7 purchase totals =	$637.02		$683.5452	$683.54	$683.55	$683.50