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	$6.40	7.670%	$6.8909	$6.89	$6.90	$6.90
Purchase #2	$13.37	3.465%	$13.8333	$13.83	$13.85	$13.80
Purchase #3	$183.83	9.221%	$200.781	$200.78	$200.80	$200.80
Purchase #4	$110.92	13.232%	$125.5969	$125.60	$125.60	$125.60
Purchase #5	$89.93	13.811%	$102.3502	$102.35	$102.35	$102.40
Purchase #6	$26.65	10.818%	$29.533	$29.53	$29.55	$29.50
Purchase #7	$105.83	5.149%	$111.2792	$111.28	$111.30	$111.30
7 purchase totals =	$536.93		$590.2645	$590.26	$590.35	$590.30