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	$7.66	12.774%	$8.6385	$8.64	$8.65	$8.60
Purchase #2	$119.46	3.511%	$123.6542	$123.65	$123.65	$123.70
Purchase #3	$91.41	9.638%	$100.2201	$100.22	$100.20	$100.20
Purchase #4	$88.32	4.776%	$92.5382	$92.54	$92.55	$92.50
Purchase #5	$59.86	6.473%	$63.7347	$63.73	$63.75	$63.70
Purchase #6	$158.52	6.534%	$168.8777	$168.88	$168.90	$168.90
Purchase #7	$12.83	10.632%	$14.1941	$14.19	$14.20	$14.20
7 purchase totals =	$538.06		$571.8575	$571.85	$571.90	$571.80