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	$45.81	9.756%	$50.2792	$50.28	$50.30	$50.30
Purchase #2	$44.68	12.627%	$50.3217	$50.32	$50.30	$50.30
Purchase #3	$88.56	8.779%	$96.3347	$96.33	$96.35	$96.30
Purchase #4	$21.25	10.584%	$23.4991	$23.50	$23.50	$23.50
Purchase #5	$100.71	4.376%	$105.1171	$105.12	$105.10	$105.10
Purchase #6	$101.92	3.823%	$105.8164	$105.82	$105.80	$105.80
Purchase #7	$114.85	13.655%	$130.5328	$130.53	$130.55	$130.50
7 purchase totals =	$517.78		$561.9010	$561.90	$561.90	$561.80