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	$100.96	13.812%	$114.9046	$114.90	$114.90	$114.90
Purchase #2	$158.58	13.174%	$179.4713	$179.47	$179.45	$179.50
Purchase #3	$95.39	4.152%	$99.3506	$99.35	$99.35	$99.40
Purchase #4	$100.44	3.466%	$103.9213	$103.92	$103.90	$103.90
Purchase #5	$127.62	11.567%	$142.3818	$142.38	$142.40	$142.40
Purchase #6	$129.80	11.772%	$145.0801	$145.08	$145.10	$145.10
Purchase #7	$35.74	4.600%	$37.384	$37.38	$37.40	$37.40
7 purchase totals =	$748.53		$822.4937	$822.48	$822.50	$822.60