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	$131.61	6.224%	$139.8014	$139.80	$139.80	$139.80
Purchase #2	$73.50	10.645%	$81.3241	$81.32	$81.30	$81.30
Purchase #3	$229.95	11.597%	$256.6173	$256.62	$256.60	$256.60
Purchase #4	$171.38	5.177%	$180.2523	$180.25	$180.25	$180.30
Purchase #5	$17.48	3.410%	$18.0761	$18.08	$18.10	$18.10
Purchase #6	$65.98	6.258%	$70.109	$70.11	$70.10	$70.10
Purchase #7	$169.83	10.301%	$187.3242	$187.32	$187.30	$187.30
7 purchase totals =	$859.73		$933.5044	$933.50	$933.45	$933.50