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	$231.35	10.715%	$256.1392	$256.14	$256.15	$256.10
Purchase #2	$39.83	5.615%	$42.0665	$42.07	$42.05	$42.10
Purchase #3	$77.88	4.629%	$81.4851	$81.49	$81.50	$81.50
Purchase #4	$70.75	10.730%	$78.3415	$78.34	$78.35	$78.30
Purchase #5	$111.40	10.582%	$123.1883	$123.19	$123.20	$123.20
Purchase #6	$236.62	6.473%	$251.9364	$251.94	$251.95	$251.90
Purchase #7	$99.36	5.322%	$104.6479	$104.65	$104.65	$104.60
7 purchase totals =	$867.19		$937.8049	$937.82	$937.85	$937.70