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	$156.60	7.487%	$168.3246	$168.32	$168.30	$168.30
Purchase #2	$102.59	10.531%	$113.3938	$113.39	$113.40	$113.40
Purchase #3	$130.35	12.446%	$146.5734	$146.57	$146.55	$146.60
Purchase #4	$112.92	5.598%	$119.2413	$119.24	$119.25	$119.20
Purchase #5	$133.40	12.159%	$149.6201	$149.62	$149.60	$149.60
Purchase #6	$183.25	4.510%	$191.5146	$191.51	$191.50	$191.50
Purchase #7	$40.65	6.857%	$43.4374	$43.44	$43.45	$43.40
7 purchase totals =	$859.76		$932.1052	$932.09	$932.05	$932.00