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	$52.97	12.501%	$59.5918	$59.59	$59.60	$59.60
Purchase #2	$177.31	10.703%	$196.2875	$196.29	$196.30	$196.30
Purchase #3	$241.45	9.163%	$263.5741	$263.57	$263.55	$263.60
Purchase #4	$233.25	9.360%	$255.0822	$255.08	$255.10	$255.10
Purchase #5	$173.46	7.680%	$186.7817	$186.78	$186.80	$186.80
Purchase #6	$197.91	8.178%	$214.0951	$214.10	$214.10	$214.10
Purchase #7	$202.55	13.456%	$229.8051	$229.81	$229.80	$229.80
7 purchase totals =	$1,278.90		$1,405.2175	$1,405.22	$1,405.25	$1,405.30