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	$206.34	6.837%	$220.4475	$220.45	$220.45	$220.40
Purchase #2	$143.82	3.726%	$149.1787	$149.18	$149.20	$149.20
Purchase #3	$49.99	10.455%	$55.2165	$55.22	$55.20	$55.20
Purchase #4	$51.90	13.720%	$59.0207	$59.02	$59.00	$59.00
Purchase #5	$201.61	10.328%	$222.4323	$222.43	$222.45	$222.40
Purchase #6	$71.92	9.723%	$78.9128	$78.91	$78.90	$78.90
Purchase #7	$226.28	9.795%	$248.4441	$248.44	$248.45	$248.40
7 purchase totals =	$951.86		$1,033.6526	$1,033.65	$1,033.65	$1,033.50