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	$19.38	9.525%	$21.2259	$21.23	$21.25	$21.20
Purchase #2	$33.82	10.672%	$37.4293	$37.43	$37.45	$37.40
Purchase #3	$213.82	10.317%	$235.8798	$235.88	$235.90	$235.90
Purchase #4	$208.61	6.143%	$221.4249	$221.42	$221.40	$221.40
Purchase #5	$134.52	8.766%	$146.312	$146.31	$146.30	$146.30
Purchase #6	$136.35	3.839%	$141.5845	$141.58	$141.60	$141.60
Purchase #7	$39.27	13.679%	$44.6417	$44.64	$44.65	$44.60
7 purchase totals =	$785.77		$848.4981	$848.49	$848.55	$848.40