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	$106.38	6.577%	$113.3766	$113.38	$113.40	$113.40
Purchase #2	$161.69	7.265%	$173.4368	$173.44	$173.45	$173.40
Purchase #3	$245.88	9.180%	$268.4518	$268.45	$268.45	$268.50
Purchase #4	$209.77	12.271%	$235.5109	$235.51	$235.50	$235.50
Purchase #5	$38.87	4.538%	$40.6339	$40.63	$40.65	$40.60
Purchase #6	$101.69	9.241%	$111.0872	$111.09	$111.10	$111.10
Purchase #7	$210.87	12.577%	$237.3911	$237.39	$237.40	$237.40
7 purchase totals =	$1,075.15		$1,179.8883	$1,179.89	$1,179.95	$1,179.90