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	$80.91	13.577%	$91.8952	$91.90	$91.90	$91.90
Purchase #2	$158.35	4.728%	$165.8368	$165.84	$165.85	$165.80
Purchase #3	$18.66	3.840%	$19.3765	$19.38	$19.40	$19.40
Purchase #4	$97.68	5.542%	$103.0934	$103.09	$103.10	$103.10
Purchase #5	$74.50	9.857%	$81.8435	$81.84	$81.85	$81.80
Purchase #6	$227.58	10.317%	$251.0594	$251.06	$251.05	$251.10
Purchase #7	$103.63	7.465%	$111.366	$111.37	$111.35	$111.40
7 purchase totals =	$761.31		$824.4708	$824.48	$824.50	$824.50