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	$134.85	3.685%	$139.8192	$139.82	$139.80	$139.80
Purchase #2	$234.31	5.720%	$247.7125	$247.71	$247.70	$247.70
Purchase #3	$171.55	4.179%	$178.7191	$178.72	$178.70	$178.70
Purchase #4	$132.28	3.760%	$137.2537	$137.25	$137.25	$137.30
Purchase #5	$235.72	8.299%	$255.2824	$255.28	$255.30	$255.30
Purchase #6	$99.26	9.345%	$108.5358	$108.54	$108.55	$108.50
Purchase #7	$150.53	13.681%	$171.124	$171.12	$171.10	$171.10
7 purchase totals =	$1,158.50		$1,238.4467	$1,238.44	$1,238.40	$1,238.40