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	$240.42	6.193%	$255.3092	$255.31	$255.30	$255.30
Purchase #2	$156.87	4.622%	$164.1205	$164.12	$164.10	$164.10
Purchase #3	$238.25	3.410%	$246.3743	$246.37	$246.35	$246.40
Purchase #4	$79.88	11.611%	$89.1549	$89.15	$89.15	$89.20
Purchase #5	$48.66	9.423%	$53.2452	$53.25	$53.25	$53.20
Purchase #6	$104.53	11.602%	$116.6576	$116.66	$116.65	$116.70
Purchase #7	$47.87	10.110%	$52.7097	$52.71	$52.70	$52.70
7 purchase totals =	$916.48		$977.5714	$977.57	$977.50	$977.60