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	$33.73	4.572%	$35.2721	$35.27	$35.25	$35.30
Purchase #2	$100.65	10.816%	$111.5363	$111.54	$111.55	$111.50
Purchase #3	$157.58	12.218%	$176.8331	$176.83	$176.85	$176.80
Purchase #4	$77.54	10.406%	$85.6088	$85.61	$85.60	$85.60
Purchase #5	$103.46	11.354%	$115.2068	$115.21	$115.20	$115.20
Purchase #6	$14.47	7.830%	$15.603	$15.60	$15.60	$15.60
Purchase #7	$19.54	9.329%	$21.3629	$21.36	$21.35	$21.40
7 purchase totals =	$506.97		$561.4230	$561.42	$561.40	$561.40