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	$28.85	10.526%	$31.8868	$31.89	$31.90	$31.90
Purchase #2	$42.44	4.743%	$44.4529	$44.45	$44.45	$44.50
Purchase #3	$130.72	13.389%	$148.2221	$148.22	$148.20	$148.20
Purchase #4	$120.94	7.364%	$129.846	$129.85	$129.85	$129.80
Purchase #5	$66.58	13.716%	$75.7121	$75.71	$75.70	$75.70
Purchase #6	$71.86	9.336%	$78.5688	$78.57	$78.55	$78.60
Purchase #7	$222.30	5.660%	$234.8822	$234.88	$234.90	$234.90
7 purchase totals =	$683.69		$743.5709	$743.57	$743.55	$743.60