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	$56.78	4.620%	$59.4032	$59.40	$59.40	$59.40
Purchase #2	$27.87	12.831%	$31.446	$31.45	$31.45	$31.40
Purchase #3	$221.97	5.837%	$234.9264	$234.93	$234.95	$234.90
Purchase #4	$212.63	13.501%	$241.3372	$241.34	$241.35	$241.30
Purchase #5	$246.36	13.414%	$279.4067	$279.41	$279.40	$279.40
Purchase #6	$63.28	7.612%	$68.0969	$68.10	$68.10	$68.10
Purchase #7	$72.60	11.461%	$80.9207	$80.92	$80.90	$80.90
7 purchase totals =	$901.49		$995.5371	$995.55	$995.55	$995.40