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	$100.83	3.232%	$104.0888	$104.09	$104.10	$104.10
Purchase #2	$87.90	13.384%	$99.6645	$99.66	$99.65	$99.70
Purchase #3	$18.36	5.589%	$19.3861	$19.39	$19.40	$19.40
Purchase #4	$119.30	7.168%	$127.8514	$127.85	$127.85	$127.90
Purchase #5	$25.64	5.626%	$27.0825	$27.08	$27.10	$27.10
Purchase #6	$116.57	3.425%	$120.5625	$120.56	$120.55	$120.60
Purchase #7	$107.79	10.273%	$118.8633	$118.86	$118.85	$118.90
7 purchase totals =	$576.39		$617.4991	$617.49	$617.50	$617.70