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	$131.41	6.187%	$139.5403	$139.54	$139.55	$139.50
Purchase #2	$243.95	5.858%	$258.2406	$258.24	$258.25	$258.20
Purchase #3	$229.48	4.681%	$240.222	$240.22	$240.20	$240.20
Purchase #4	$11.26	5.684%	$11.9	$11.90	$11.90	$11.90
Purchase #5	$163.83	4.857%	$171.7872	$171.79	$171.80	$171.80
Purchase #6	$100.52	12.279%	$112.8629	$112.86	$112.85	$112.90
Purchase #7	$22.38	13.510%	$25.4035	$25.40	$25.40	$25.40
7 purchase totals =	$902.83		$959.9565	$959.95	$959.95	$959.90