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	$171.59	8.120%	$185.5231	$185.52	$185.50	$185.50
Purchase #2	$110.42	7.303%	$118.484	$118.48	$118.50	$118.50
Purchase #3	$15.40	12.184%	$17.2763	$17.28	$17.30	$17.30
Purchase #4	$21.39	12.522%	$24.0685	$24.07	$24.05	$24.10
Purchase #5	$147.40	5.777%	$155.9153	$155.92	$155.90	$155.90
Purchase #6	$84.63	4.831%	$88.7185	$88.72	$88.70	$88.70
Purchase #7	$15.54	12.710%	$17.5151	$17.52	$17.50	$17.50
7 purchase totals =	$566.37		$607.5008	$607.51	$607.45	$607.50