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	$124.67	11.526%	$139.0395	$139.04	$139.05	$139.00
Purchase #2	$182.32	7.868%	$196.6649	$196.66	$196.65	$196.70
Purchase #3	$40.97	8.163%	$44.3144	$44.31	$44.30	$44.30
Purchase #4	$203.79	12.501%	$229.2658	$229.27	$229.25	$229.30
Purchase #5	$193.64	5.106%	$203.5273	$203.53	$203.55	$203.50
Purchase #6	$141.40	7.207%	$151.5907	$151.59	$151.60	$151.60
Purchase #7	$48.60	13.584%	$55.2018	$55.20	$55.20	$55.20
7 purchase totals =	$935.39		$1,019.6044	$1,019.60	$1,019.60	$1,019.60