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	$70.47	11.798%	$78.7841	$78.78	$78.80	$78.80
Purchase #2	$240.56	4.725%	$251.9265	$251.93	$251.95	$251.90
Purchase #3	$20.58	3.333%	$21.2659	$21.27	$21.25	$21.30
Purchase #4	$194.36	6.395%	$206.7893	$206.79	$206.80	$206.80
Purchase #5	$162.89	7.603%	$175.2745	$175.27	$175.25	$175.30
Purchase #6	$83.81	8.219%	$90.6983	$90.70	$90.70	$90.70
Purchase #7	$224.48	13.537%	$254.8679	$254.87	$254.85	$254.90
7 purchase totals =	$997.15		$1,079.6065	$1,079.61	$1,079.60	$1,079.70