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	$115.26	12.666%	$129.8588	$129.86	$129.85	$129.90
Purchase #2	$103.48	3.703%	$107.3119	$107.31	$107.30	$107.30
Purchase #3	$71.71	9.501%	$78.5232	$78.52	$78.50	$78.50
Purchase #4	$47.88	12.113%	$53.6797	$53.68	$53.70	$53.70
Purchase #5	$196.82	6.124%	$208.8733	$208.87	$208.85	$208.90
Purchase #6	$125.39	4.847%	$131.4677	$131.47	$131.45	$131.50
Purchase #7	$100.40	13.335%	$113.7883	$113.79	$113.80	$113.80
7 purchase totals =	$760.94		$823.5029	$823.50	$823.45	$823.60