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	$126.36	13.385%	$143.2733	$143.27	$143.25	$143.30
Purchase #2	$181.88	9.214%	$198.6384	$198.64	$198.65	$198.60
Purchase #3	$57.42	3.265%	$59.2948	$59.29	$59.30	$59.30
Purchase #4	$123.45	6.425%	$131.3817	$131.38	$131.40	$131.40
Purchase #5	$134.66	6.595%	$143.5408	$143.54	$143.55	$143.50
Purchase #6	$193.95	9.698%	$212.7593	$212.76	$212.75	$212.80
Purchase #7	$163.39	11.820%	$182.7027	$182.70	$182.70	$182.70
7 purchase totals =	$981.11		$1,071.5910	$1,071.58	$1,071.60	$1,071.60