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	$23.41	3.766%	$24.2916	$24.29	$24.30	$24.30
Purchase #2	$139.56	10.653%	$154.4273	$154.43	$154.45	$154.40
Purchase #3	$96.72	13.324%	$109.607	$109.61	$109.60	$109.60
Purchase #4	$166.61	5.343%	$175.512	$175.51	$175.50	$175.50
Purchase #5	$59.53	5.874%	$63.0268	$63.03	$63.05	$63.00
Purchase #6	$175.27	13.418%	$198.7877	$198.79	$198.80	$198.80
Purchase #7	$140.31	13.245%	$158.8941	$158.89	$158.90	$158.90
7 purchase totals =	$801.41		$884.5465	$884.55	$884.60	$884.50