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	$226.70	13.106%	$256.4113	$256.41	$256.40	$256.40
Purchase #2	$110.93	5.203%	$116.7017	$116.70	$116.70	$116.70
Purchase #3	$141.43	10.341%	$156.0553	$156.06	$156.05	$156.10
Purchase #4	$84.28	9.602%	$92.3726	$92.37	$92.35	$92.40
Purchase #5	$170.27	9.558%	$186.5444	$186.54	$186.55	$186.50
Purchase #6	$53.40	12.247%	$59.9399	$59.94	$59.95	$59.90
Purchase #7	$231.66	13.686%	$263.365	$263.37	$263.35	$263.40
7 purchase totals =	$1,018.67		$1,131.3902	$1,131.39	$1,131.35	$1,131.40