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	$38.91	4.838%	$40.7925	$40.79	$40.80	$40.80
Purchase #2	$226.57	5.736%	$239.5661	$239.57	$239.55	$239.60
Purchase #3	$54.70	12.797%	$61.7	$61.70	$61.70	$61.70
Purchase #4	$40.59	9.862%	$44.593	$44.59	$44.60	$44.60
Purchase #5	$42.54	13.147%	$48.1327	$48.13	$48.15	$48.10
Purchase #6	$65.64	8.406%	$71.1577	$71.16	$71.15	$71.20
Purchase #7	$102.46	11.541%	$114.2849	$114.28	$114.30	$114.30
7 purchase totals =	$571.41		$620.2269	$620.22	$620.25	$620.30