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	$247.78	13.114%	$280.2739	$280.27	$280.25	$280.30
Purchase #2	$187.65	3.715%	$194.6212	$194.62	$194.60	$194.60
Purchase #3	$215.76	10.570%	$238.5658	$238.57	$238.55	$238.60
Purchase #4	$67.88	5.678%	$71.7342	$71.73	$71.75	$71.70
Purchase #5	$222.35	3.544%	$230.2301	$230.23	$230.25	$230.20
Purchase #6	$249.89	11.873%	$279.5594	$279.56	$279.55	$279.60
Purchase #7	$244.89	9.336%	$267.7529	$267.75	$267.75	$267.80
7 purchase totals =	$1,436.20		$1,562.7375	$1,562.73	$1,562.70	$1,562.80