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	$79.62	12.324%	$89.4324	$89.43	$89.45	$89.40
Purchase #2	$165.40	10.587%	$182.9109	$182.91	$182.90	$182.90
Purchase #3	$100.70	3.210%	$103.9325	$103.93	$103.95	$103.90
Purchase #4	$202.32	11.469%	$225.5241	$225.52	$225.50	$225.50
Purchase #5	$208.49	10.720%	$230.8401	$230.84	$230.85	$230.80
Purchase #6	$104.94	13.420%	$119.0229	$119.02	$119.00	$119.00
Purchase #7	$224.43	4.641%	$234.8458	$234.85	$234.85	$234.80
7 purchase totals =	$1,085.90		$1,186.5087	$1,186.50	$1,186.50	$1,186.30