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	$188.54	13.603%	$214.1871	$214.19	$214.20	$214.20
Purchase #2	$97.51	12.407%	$109.6081	$109.61	$109.60	$109.60
Purchase #3	$29.69	6.828%	$31.7172	$31.72	$31.70	$31.70
Purchase #4	$73.52	9.207%	$80.289	$80.29	$80.30	$80.30
Purchase #5	$164.64	12.139%	$184.6256	$184.63	$184.65	$184.60
Purchase #6	$29.82	9.858%	$32.7597	$32.76	$32.75	$32.80
Purchase #7	$62.84	7.618%	$67.6272	$67.63	$67.65	$67.60
7 purchase totals =	$646.56		$720.8139	$720.83	$720.85	$720.80