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	$125.67	10.779%	$139.216	$139.22	$139.20	$139.20
Purchase #2	$159.61	13.503%	$181.1621	$181.16	$181.15	$181.20
Purchase #3	$177.42	7.146%	$190.0984	$190.10	$190.10	$190.10
Purchase #4	$148.82	8.128%	$160.9161	$160.92	$160.90	$160.90
Purchase #5	$95.32	8.651%	$103.5661	$103.57	$103.55	$103.60
Purchase #6	$152.50	8.158%	$164.941	$164.94	$164.95	$164.90
Purchase #7	$35.35	12.582%	$39.7977	$39.80	$39.80	$39.80
7 purchase totals =	$894.69		$979.6974	$979.71	$979.65	$979.70