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	$140.42	3.688%	$145.5987	$145.60	$145.60	$145.60
Purchase #2	$119.72	4.795%	$125.4606	$125.46	$125.45	$125.50
Purchase #3	$244.70	11.722%	$273.3837	$273.38	$273.40	$273.40
Purchase #4	$57.64	6.710%	$61.5076	$61.51	$61.50	$61.50
Purchase #5	$89.46	10.390%	$98.7549	$98.75	$98.75	$98.80
Purchase #6	$74.73	3.139%	$77.0758	$77.08	$77.10	$77.10
Purchase #7	$34.56	11.167%	$38.4193	$38.42	$38.40	$38.40
7 purchase totals =	$761.23		$820.2006	$820.20	$820.20	$820.30