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	$23.35	4.206%	$24.3321	$24.33	$24.35	$24.30
Purchase #2	$97.37	12.174%	$109.2238	$109.22	$109.20	$109.20
Purchase #3	$28.99	11.199%	$32.2366	$32.24	$32.25	$32.20
Purchase #4	$151.47	4.161%	$157.7727	$157.77	$157.75	$157.80
Purchase #5	$104.93	13.840%	$119.4523	$119.45	$119.45	$119.50
Purchase #6	$81.31	10.245%	$89.6402	$89.64	$89.65	$89.60
Purchase #7	$105.47	10.157%	$116.1826	$116.18	$116.20	$116.20
7 purchase totals =	$592.89		$648.8403	$648.83	$648.85	$648.80