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	$146.75	5.830%	$155.3055	$155.31	$155.30	$155.30
Purchase #2	$48.67	11.301%	$54.1702	$54.17	$54.15	$54.20
Purchase #3	$57.40	7.161%	$61.5104	$61.51	$61.50	$61.50
Purchase #4	$38.32	6.840%	$40.9411	$40.94	$40.95	$40.90
Purchase #5	$61.82	12.817%	$69.7435	$69.74	$69.75	$69.70
Purchase #6	$29.58	5.629%	$31.2451	$31.25	$31.25	$31.20
Purchase #7	$154.82	7.641%	$166.6498	$166.65	$166.65	$166.60
7 purchase totals =	$537.36		$579.5656	$579.57	$579.55	$579.40