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	$104.56	7.823%	$112.7397	$112.74	$112.75	$112.70
Purchase #2	$38.89	4.419%	$40.6085	$40.61	$40.60	$40.60
Purchase #3	$240.90	8.598%	$261.6126	$261.61	$261.60	$261.60
Purchase #4	$178.62	6.456%	$190.1517	$190.15	$190.15	$190.20
Purchase #5	$147.88	12.411%	$166.2334	$166.23	$166.25	$166.20
Purchase #6	$50.49	13.621%	$57.3672	$57.37	$57.35	$57.40
Purchase #7	$59.86	12.380%	$67.2707	$67.27	$67.25	$67.30
7 purchase totals =	$821.20		$895.9838	$895.98	$895.95	$896.00