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	$208.57	4.628%	$218.2226	$218.22	$218.20	$218.20
Purchase #2	$207.54	7.368%	$222.8315	$222.83	$222.85	$222.80
Purchase #3	$116.65	12.761%	$131.5357	$131.54	$131.55	$131.50
Purchase #4	$46.40	4.193%	$48.3456	$48.35	$48.35	$48.30
Purchase #5	$133.84	8.449%	$145.1481	$145.15	$145.15	$145.10
Purchase #6	$36.41	6.502%	$38.7774	$38.78	$38.80	$38.80
Purchase #7	$71.30	13.857%	$81.18	$81.18	$81.20	$81.20
7 purchase totals =	$820.71		$886.0409	$886.05	$886.10	$885.90