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	$37.85	12.387%	$42.5385	$42.54	$42.55	$42.50
Purchase #2	$87.69	11.263%	$97.5665	$97.57	$97.55	$97.60
Purchase #3	$109.43	10.159%	$120.547	$120.55	$120.55	$120.50
Purchase #4	$17.30	5.300%	$18.2169	$18.22	$18.20	$18.20
Purchase #5	$6.35	5.385%	$6.6919	$6.69	$6.70	$6.70
Purchase #6	$24.47	13.715%	$27.8261	$27.83	$27.85	$27.80
Purchase #7	$54.31	5.298%	$57.1873	$57.19	$57.20	$57.20
7 purchase totals =	$337.40		$370.5742	$370.59	$370.60	$370.50