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	$33.90	13.305%	$38.4104	$38.41	$38.40	$38.40
Purchase #2	$118.93	10.589%	$131.5235	$131.52	$131.50	$131.50
Purchase #3	$74.67	8.266%	$80.8422	$80.84	$80.85	$80.80
Purchase #4	$95.63	9.473%	$104.689	$104.69	$104.70	$104.70
Purchase #5	$241.88	4.173%	$251.9737	$251.97	$251.95	$252.00
Purchase #6	$207.76	10.634%	$229.8532	$229.85	$229.85	$229.90
Purchase #7	$162.94	5.801%	$172.3921	$172.39	$172.40	$172.40
7 purchase totals =	$935.71		$1,009.6841	$1,009.67	$1,009.65	$1,009.70