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	$123.79	11.224%	$137.6842	$137.68	$137.70	$137.70
Purchase #2	$48.52	10.838%	$53.7786	$53.78	$53.80	$53.80
Purchase #3	$79.88	6.423%	$85.0107	$85.01	$85.00	$85.00
Purchase #4	$111.44	11.240%	$123.9659	$123.97	$123.95	$124.00
Purchase #5	$43.40	9.662%	$47.5933	$47.59	$47.60	$47.60
Purchase #6	$250.29	11.767%	$279.7416	$279.74	$279.75	$279.70
Purchase #7	$214.94	10.787%	$238.1256	$238.13	$238.15	$238.10
7 purchase totals =	$872.26		$965.8999	$965.90	$965.95	$965.90