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	$166.55	10.121%	$183.4065	$183.41	$183.40	$183.40
Purchase #2	$52.29	13.653%	$59.4292	$59.43	$59.45	$59.40
Purchase #3	$53.97	3.103%	$55.6447	$55.64	$55.65	$55.60
Purchase #4	$110.94	5.747%	$117.3157	$117.32	$117.30	$117.30
Purchase #5	$167.82	9.520%	$183.7965	$183.80	$183.80	$183.80
Purchase #6	$132.37	7.434%	$142.2104	$142.21	$142.20	$142.20
Purchase #7	$191.91	3.290%	$198.2238	$198.22	$198.20	$198.20
7 purchase totals =	$875.85		$940.0268	$940.03	$940.00	$939.90