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	$94.60	9.752%	$103.8254	$103.83	$103.85	$103.80
Purchase #2	$64.74	8.128%	$70.0021	$70.00	$70.00	$70.00
Purchase #3	$87.73	3.534%	$90.8304	$90.83	$90.85	$90.80
Purchase #4	$57.33	11.528%	$63.939	$63.94	$63.95	$63.90
Purchase #5	$47.40	10.407%	$52.3329	$52.33	$52.35	$52.30
Purchase #6	$83.66	3.250%	$86.379	$86.38	$86.40	$86.40
Purchase #7	$99.27	10.321%	$109.5157	$109.52	$109.50	$109.50
7 purchase totals =	$534.73		$576.8245	$576.83	$576.90	$576.70