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	$17.48	6.745%	$18.659	$18.66	$18.65	$18.70
Purchase #2	$182.46	3.788%	$189.3716	$189.37	$189.35	$189.40
Purchase #3	$91.83	11.477%	$102.3693	$102.37	$102.35	$102.40
Purchase #4	$105.66	9.622%	$115.8266	$115.83	$115.85	$115.80
Purchase #5	$100.30	4.167%	$104.4795	$104.48	$104.50	$104.50
Purchase #6	$88.38	13.752%	$100.534	$100.53	$100.55	$100.50
Purchase #7	$45.57	7.799%	$49.124	$49.12	$49.10	$49.10
7 purchase totals =	$631.68		$680.3640	$680.36	$680.35	$680.40