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	$123.77	13.627%	$140.6361	$140.64	$140.65	$140.60
Purchase #2	$64.60	3.786%	$67.0458	$67.05	$67.05	$67.00
Purchase #3	$92.52	11.554%	$103.2098	$103.21	$103.20	$103.20
Purchase #4	$80.64	7.660%	$86.817	$86.82	$86.80	$86.80
Purchase #5	$151.52	9.696%	$166.2114	$166.21	$166.20	$166.20
Purchase #6	$47.29	12.388%	$53.1483	$53.15	$53.15	$53.10
Purchase #7	$172.86	3.254%	$178.4849	$178.48	$178.50	$178.50
7 purchase totals =	$733.20		$795.5533	$795.56	$795.55	$795.40